How does this function create a nested object? - javascript

I have been using a version of the function below to create and/or add values to nested objects:
function assign(obj, keyPath, value) {
const lastKeyIndex = keyPath.length-1;
for (let i = 0; i < lastKeyIndex; ++ i) {
const key = keyPath[i];
if (!(key in obj)){
obj[key] = {}
}
obj = obj[key];
}
obj[keyPath[lastKeyIndex]] = value;
}
(Posted in 2011 by kennytm, slightly modified above:
Javascript: how to dynamically create nested objects using object names given by an array).
Example usage to specify a value in which the keys represent the (0) database
name, (1) table name, (3) id value, and (4) column name:
let obj = {}
assign(obj, ['farm', 'products', '25', 'product_name'], 'lettuce');
console.log(JSON.stringify(obj));
/* (reformatted)
{
"farm": {
"products": {
"25": {
"product_name":"lettuce"
}
}
}
}
*/
We can add a second value for the same row:
assign(obj, ['farm', 'products', '25', 'product_unit'], 'head');
console.log(JSON.stringify(obj));
/* (reformatted)
{
"farm": {
"products": {
"25": {
"product_name":"lettuce",
"product_unit":"head"
}
}
}
}
*/
Or additional values from different rows, tables, and databases:
assign(obj, ['farm', 'equipment', '17', 'equipment_name'], 'tractor');
console.log(JSON.stringify(obj));
/* (reformatted)
{
"farm": {
"products": {
"25": {
"product_name": "lettuce",
"product_unit": "head"
}
},
"equipment": {
"17": {
"equipment_name": "tractor"
}
}
}
}
*/
The function works perfectly but I can't figure out how it manages to aggregate the key path. It would appear to simply create or replace an existing object with an object consisting of only the last key and the value. In fact, if I execute the same statements not inside a function and without using a loop, the statements do exactly that.
(Starting with assignment of the first value to an empty object):
let obj = {}
let key;
// first iteration of the function's loop
key = 'farm';
if (!(key in obj)) {
obj[key] = {}
}
obj = obj[key];
// second iteration
key = 'products';
if (!(key in obj)) {
obj[key] = {}
}
obj = obj[key];
// third iteration
key = '25';
if (!(key in obj)) {
obj[key] = {}
}
obj = obj[key];
// final line from the function
obj['product name'] = 'lettuce';
console.log(JSON.stringify(obj));
// {"product name":"lettuce"}
As you can see, the object is not nested but simply replaced at each step.
What magic makes the function work differently?

The difference is that you didn't save a variable with a reference to the original object. When you reassign obj, you no longer have a variable containing the parent.
When using the function, that variable is in the function caller. Reassigning the local variable obj has no effect on the caller's variable.
To emulate this in your manual steps, change the beginning to:
const original = {};
let obj = original;
This is analogous to the way the function parameter is passed.
Then at the very end, do
console.log(JSON.stringify(original));
and you should see the whole object with all the nested properties added.

Related

Call functions from function inside an object using for-in Loop(object literal) [duplicate]

I'd like to traverse a JSON object tree, but cannot find any library for that. It doesn't seem difficult but it feels like reinventing the wheel.
In XML there are so many tutorials showing how to traverse an XML tree with DOM :(
If you think jQuery is kind of overkill for such a primitive task, you could do something like that:
//your object
var o = {
foo:"bar",
arr:[1,2,3],
subo: {
foo2:"bar2"
}
};
//called with every property and its value
function process(key,value) {
console.log(key + " : "+value);
}
function traverse(o,func) {
for (var i in o) {
func.apply(this,[i,o[i]]);
if (o[i] !== null && typeof(o[i])=="object") {
//going one step down in the object tree!!
traverse(o[i],func);
}
}
}
//that's all... no magic, no bloated framework
traverse(o,process);
A JSON object is simply a Javascript object. That's actually what JSON stands for: JavaScript Object Notation. So you'd traverse a JSON object however you'd choose to "traverse" a Javascript object in general.
In ES2017 you would do:
Object.entries(jsonObj).forEach(([key, value]) => {
// do something with key and val
});
You can always write a function to recursively descend into the object:
function traverse(jsonObj) {
if( jsonObj !== null && typeof jsonObj == "object" ) {
Object.entries(jsonObj).forEach(([key, value]) => {
// key is either an array index or object key
traverse(value);
});
}
else {
// jsonObj is a number or string
}
}
This should be a good starting point. I highly recommend using modern javascript methods for such things, since they make writing such code much easier.
function traverse(o) {
for (var i in o) {
if (!!o[i] && typeof(o[i])=="object") {
console.log(i, o[i]);
traverse(o[i]);
} else {
console.log(i, o[i]);
}
}
}
There's a new library for traversing JSON data with JavaScript that supports many different use cases.
https://npmjs.org/package/traverse
https://github.com/substack/js-traverse
It works with all kinds of JavaScript objects. It even detects cycles.
It provides the path of each node, too.
Original Simplified Answer
For a newer way to do it if you don't mind dropping IE and mainly supporting more current browsers (check kangax's es6 table for compatibility). You can use es2015 generators for this. I've updated #TheHippo's answer accordingly. Of course if you really want IE support you can use the babel JavaScript transpiler.
// Implementation of Traverse
function* traverse(o, path=[]) {
for (var i in o) {
const itemPath = path.concat(i);
yield [i,o[i],itemPath,o];
if (o[i] !== null && typeof(o[i])=="object") {
//going one step down in the object tree!!
yield* traverse(o[i], itemPath);
}
}
}
// Traverse usage:
//that's all... no magic, no bloated framework
for(var [key, value, path, parent] of traverse({
foo:"bar",
arr:[1,2,3],
subo: {
foo2:"bar2"
}
})) {
// do something here with each key and value
console.log(key, value, path, parent);
}
If you want only own enumerable properties (basically non-prototype chain properties) you can change it to iterate using Object.keys and a for...of loop instead:
function* traverse(o,path=[]) {
for (var i of Object.keys(o)) {
const itemPath = path.concat(i);
yield [i,o[i],itemPath,o];
if (o[i] !== null && typeof(o[i])=="object") {
//going one step down in the object tree!!
yield* traverse(o[i],itemPath);
}
}
}
//that's all... no magic, no bloated framework
for(var [key, value, path, parent] of traverse({
foo:"bar",
arr:[1,2,3],
subo: {
foo2:"bar2"
}
})) {
// do something here with each key and value
console.log(key, value, path, parent);
}
EDIT: This edited answer solves infinite looping traversals.
Stopping Pesky Infinite Object Traversals
This edited answer still provides one of the added benefits of my original answer which allows you to use the provided generator function in order to use a cleaner and simple iterable interface (think using for of loops as in for(var a of b) where b is an iterable and a is an element of the iterable). By using the generator function along with being a simpler api it also helps with code reuse by making it so you don't have to repeat the iteration logic everywhere you want to iterate deeply on an object's properties and it also makes it possible to break out of the loop if you would like to stop iteration earlier.
One thing that I notice that has not been addressed and that isn't in my original answer is that you should be careful traversing arbitrary (i.e. any "random" set of) objects, because JavaScript objects can be self referencing. This creates the opportunity to have infinite looping traversals. Unmodified JSON data however cannot be self referencing, so if you are using this particular subset of JS objects you don't have to worry about infinite looping traversals and you can refer to my original answer or other answers. Here is an example of a non-ending traversal (note it is not a runnable piece of code, because otherwise it would crash your browser tab).
Also in the generator object in my edited example I opted to use Object.keys instead of for in which iterates only non-prototype keys on the object. You can swap this out yourself if you want the prototype keys included. See my original answer section below for both implementations with Object.keys and for in.
Worse - This will infinite loop on self-referential objects:
function* traverse(o, path=[]) {
for (var i of Object.keys(o)) {
const itemPath = path.concat(i);
yield [i,o[i],itemPath, o];
if (o[i] !== null && typeof(o[i])=="object") {
//going one step down in the object tree!!
yield* traverse(o[i], itemPath);
}
}
}
//your object
var o = {
foo:"bar",
arr:[1,2,3],
subo: {
foo2:"bar2"
}
};
// this self-referential property assignment is the only real logical difference
// from the above original example which ends up making this naive traversal
// non-terminating (i.e. it makes it infinite loop)
o.o = o;
//that's all... no magic, no bloated framework
for(var [key, value, path, parent] of traverse(o)) {
// do something here with each key and value
console.log(key, value, path, parent);
}
To save yourself from this you can add a set within a closure, so that when the function is first called it starts to build a memory of the objects it has seen and does not continue iteration once it comes across an already seen object. The below code snippet does that and thus handles infinite looping cases.
Better - This will not infinite loop on self-referential objects:
function* traverse(o) {
const memory = new Set();
function * innerTraversal (o, path=[]) {
if(memory.has(o)) {
// we've seen this object before don't iterate it
return;
}
// add the new object to our memory.
memory.add(o);
for (var i of Object.keys(o)) {
const itemPath = path.concat(i);
yield [i,o[i],itemPath, o];
if (o[i] !== null && typeof(o[i])=="object") {
//going one step down in the object tree!!
yield* innerTraversal(o[i], itemPath);
}
}
}
yield* innerTraversal(o);
}
//your object
var o = {
foo:"bar",
arr:[1,2,3],
subo: {
foo2:"bar2"
}
};
/// this self-referential property assignment is the only real logical difference
// from the above original example which makes more naive traversals
// non-terminating (i.e. it makes it infinite loop)
o.o = o;
console.log(o);
//that's all... no magic, no bloated framework
for(var [key, value, path, parent] of traverse(o)) {
// do something here with each key and value
console.log(key, value, path, parent);
}
EDIT: All above examples in this answer have been edited to include a new path variable yielded from the iterator as per #supersan's request. The path variable is an array of strings where each string in the array represents each key that was accessed to get to the resulting iterated value from the original source object. The path variable can be fed into lodash's get function/method. Or you could write your own version of lodash's get which handles only arrays like so:
function get (object, path) {
return path.reduce((obj, pathItem) => obj ? obj[pathItem] : undefined, object);
}
const example = {a: [1,2,3], b: 4, c: { d: ["foo"] }};
// these paths exist on the object
console.log(get(example, ["a", "0"]));
console.log(get(example, ["c", "d", "0"]));
console.log(get(example, ["b"]));
// these paths do not exist on the object
console.log(get(example, ["e", "f", "g"]));
console.log(get(example, ["b", "f", "g"]));
You could also make a set function like so:
function set (object, path, value) {
const obj = path.slice(0,-1).reduce((obj, pathItem) => obj ? obj[pathItem] : undefined, object)
if(obj && obj[path[path.length - 1]]) {
obj[path[path.length - 1]] = value;
}
return object;
}
const example = {a: [1,2,3], b: 4, c: { d: ["foo"] }};
// these paths exist on the object
console.log(set(example, ["a", "0"], 2));
console.log(set(example, ["c", "d", "0"], "qux"));
console.log(set(example, ["b"], 12));
// these paths do not exist on the object
console.log(set(example, ["e", "f", "g"], false));
console.log(set(example, ["b", "f", "g"], null));
EDIT Sep. 2020: I added a parent for quicker access of the previous object. This could allow you to more quickly build a reverse traverser. Also you could always modify the traversal algorithm to do breadth first search instead of depth first which is actually probably more predictable in fact here's a TypeScript version with Breadth First Search. Since this is a JavaScript question I'll put the JS version here:
var TraverseFilter;
(function (TraverseFilter) {
/** prevents the children from being iterated. */
TraverseFilter["reject"] = "reject";
})(TraverseFilter || (TraverseFilter = {}));
function* traverse(o) {
const memory = new Set();
function* innerTraversal(root) {
const queue = [];
queue.push([root, []]);
while (queue.length > 0) {
const [o, path] = queue.shift();
if (memory.has(o)) {
// we've seen this object before don't iterate it
continue;
}
// add the new object to our memory.
memory.add(o);
for (var i of Object.keys(o)) {
const item = o[i];
const itemPath = path.concat([i]);
const filter = yield [i, item, itemPath, o];
if (filter === TraverseFilter.reject)
continue;
if (item !== null && typeof item === "object") {
//going one step down in the object tree!!
queue.push([item, itemPath]);
}
}
}
}
yield* innerTraversal(o);
}
//your object
var o = {
foo: "bar",
arr: [1, 2, 3],
subo: {
foo2: "bar2"
}
};
/// this self-referential property assignment is the only real logical difference
// from the above original example which makes more naive traversals
// non-terminating (i.e. it makes it infinite loop)
o.o = o;
//that's all... no magic, no bloated framework
for (const [key, value, path, parent] of traverse(o)) {
// do something here with each key and value
console.log(key, value, path, parent);
}
Depends on what you want to do. Here's an example of traversing a JavaScript object tree, printing keys and values as it goes:
function js_traverse(o) {
var type = typeof o
if (type == "object") {
for (var key in o) {
print("key: ", key)
js_traverse(o[key])
}
} else {
print(o)
}
}
js> foobar = {foo: "bar", baz: "quux", zot: [1, 2, 3, {some: "hash"}]}
[object Object]
js> js_traverse(foobar)
key: foo
bar
key: baz
quux
key: zot
key: 0
1
key: 1
2
key: 2
3
key: 3
key: some
hash
If you're traversing an actual JSON string then you can use a reviver function.
function traverse (json, callback) {
JSON.parse(json, function (key, value) {
if (key !== '') {
callback.call(this, key, value)
}
return value
})
}
traverse('{"a":{"b":{"c":{"d":1}},"e":{"f":2}}}', function (key, value) {
console.log(arguments)
})
When traversing an object:
function traverse (obj, callback, trail) {
trail = trail || []
Object.keys(obj).forEach(function (key) {
var value = obj[key]
if (Object.getPrototypeOf(value) === Object.prototype) {
traverse(value, callback, trail.concat(key))
} else {
callback.call(obj, key, value, trail)
}
})
}
traverse({a: {b: {c: {d: 1}}, e: {f: 2}}}, function (key, value, trail) {
console.log(arguments)
})
I wanted to use the perfect solution of #TheHippo in an anonymous function, without use of process and trigger functions. The following worked for me, sharing for novice programmers like myself.
(function traverse(o) {
for (var i in o) {
console.log('key : ' + i + ', value: ' + o[i]);
if (o[i] !== null && typeof(o[i])=="object") {
//going on step down in the object tree!!
traverse(o[i]);
}
}
})
(json);
Most Javascript engines do not optimize tail recursion (this might not be an issue if your JSON isn't deeply nested), but I usually err on the side of caution and do iteration instead, e.g.
function traverse(o, fn) {
const stack = [o]
while (stack.length) {
const obj = stack.shift()
Object.keys(obj).forEach((key) => {
fn(key, obj[key], obj)
if (obj[key] instanceof Object) {
stack.unshift(obj[key])
return
}
})
}
}
const o = {
name: 'Max',
legal: false,
other: {
name: 'Maxwell',
nested: {
legal: true
}
}
}
const fx = (key, value, obj) => console.log(key, value)
traverse(o, fx)
My Script:
op_needed = [];
callback_func = function(val) {
var i, j, len;
results = [];
for (j = 0, len = val.length; j < len; j++) {
i = val[j];
if (i['children'].length !== 0) {
call_func(i['children']);
} else {
op_needed.push(i['rel_path']);
}
}
return op_needed;
};
Input JSON:
[
{
"id": null,
"name": "output",
"asset_type_assoc": [],
"rel_path": "output",
"children": [
{
"id": null,
"name": "output",
"asset_type_assoc": [],
"rel_path": "output/f1",
"children": [
{
"id": null,
"name": "v#",
"asset_type_assoc": [],
"rel_path": "output/f1/ver",
"children": []
}
]
}
]
}
]
Function Call:
callback_func(inp_json);
Output as per my Need:
["output/f1/ver"]
var test = {
depth00: {
depth10: 'string'
, depth11: 11
, depth12: {
depth20:'string'
, depth21:21
}
, depth13: [
{
depth22:'2201'
, depth23:'2301'
}
, {
depth22:'2202'
, depth23:'2302'
}
]
}
,depth01: {
depth10: 'string'
, depth11: 11
, depth12: {
depth20:'string'
, depth21:21
}
, depth13: [
{
depth22:'2201'
, depth23:'2301'
}
, {
depth22:'2202'
, depth23:'2302'
}
]
}
, depth02: 'string'
, dpeth03: 3
};
function traverse(result, obj, preKey) {
if(!obj) return [];
if (typeof obj == 'object') {
for(var key in obj) {
traverse(result, obj[key], (preKey || '') + (preKey ? '[' + key + ']' : key))
}
} else {
result.push({
key: (preKey || '')
, val: obj
});
}
return result;
}
document.getElementById('textarea').value = JSON.stringify(traverse([], test), null, 2);
<textarea style="width:100%;height:600px;" id="textarea"></textarea>
I've created library to traverse and edit deep nested JS objects. Check out API here: https://github.com/dominik791
You can also play with the library interactively using demo app:
https://dominik791.github.io/obj-traverse-demo/
Examples of usage:
You should always have root object which is the first parameter of each method:
var rootObj = {
name: 'rootObject',
children: [
{
'name': 'child1',
children: [ ... ]
},
{
'name': 'child2',
children: [ ... ]
}
]
};
The second parameter is always the name of property that holds nested objects. In above case it would be 'children'.
The third parameter is an object that you use to find object/objects that you want to find/modify/delete. For example if you're looking for object with id equal to 1, then you will pass { id: 1} as the third parameter.
And you can:
findFirst(rootObj, 'children', { id: 1 }) to find first object
with id === 1
findAll(rootObj, 'children', { id: 1 }) to find all objects
with id === 1
findAndDeleteFirst(rootObj, 'children', { id: 1 }) to delete first matching object
findAndDeleteAll(rootObj, 'children', { id: 1 }) to delete all matching objects
replacementObj is used as the last parameter in two last methods:
findAndModifyFirst(rootObj, 'children', { id: 1 }, { id: 2, name: 'newObj'}) to change first found object with id === 1 to the { id: 2, name: 'newObj'}
findAndModifyAll(rootObj, 'children', { id: 1 }, { id: 2, name: 'newObj'}) to change all objects with id === 1 to the { id: 2, name: 'newObj'}
We use object-scan for many data processing tasks. It's powerful once you wrap your head around it. Here is how you could do basic traversal
// const objectScan = require('object-scan');
const obj = { foo: 'bar', arr: [1, 2, 3], subo: { foo2: 'bar2' } };
objectScan(['**'], {
reverse: false,
filterFn: ({ key, value }) => {
console.log(key, value);
}
})(obj);
// => [ 'foo' ] bar
// => [ 'arr', 0 ] 1
// => [ 'arr', 1 ] 2
// => [ 'arr', 2 ] 3
// => [ 'arr' ] [ 1, 2, 3 ]
// => [ 'subo', 'foo2' ] bar2
// => [ 'subo' ] { foo2: 'bar2' }
.as-console-wrapper {max-height: 100% !important; top: 0}
<script src="https://bundle.run/object-scan#13.8.0"></script>
Disclaimer: I'm the author of object-scan
This Will read All Nodes to a map.
function readJsonFile() {
let jsonString = getValueById("testDataContent");
let jsonObj = JSON.parse(jsonString);
let jsonElements = [];
jsonElements = traverse(jsonObj, jsonElements);
console.log(jsonElements)
}
function traverse(jsonObj, jsonElements) {
if (jsonObj !== null && typeof jsonObj == "object") {
Object.entries(jsonObj).forEach(([key, value]) => {
if (typeof value == "object") {
var obj = [];
let map = new Map();
map.set(key, traverse(value, obj))
jsonElements.push(map);
} else {
var obj = [];
obj.key = key;
obj.value = value;
jsonElements.push(obj);
}
});
} else {
}
return jsonElements;
}
You can get all keys / values and preserve the hierarchy with this
// get keys of an object or array
function getkeys(z){
var out=[];
for(var i in z){out.push(i)};
return out;
}
// print all inside an object
function allInternalObjs(data, name) {
name = name || 'data';
return getkeys(data).reduce(function(olist, k){
var v = data[k];
if(typeof v === 'object') { olist.push.apply(olist, allInternalObjs(v, name + '.' + k)); }
else { olist.push(name + '.' + k + ' = ' + v); }
return olist;
}, []);
}
// run with this
allInternalObjs({'a':[{'b':'c'},{'d':{'e':5}}],'f':{'g':'h'}}, 'ob')
This is a modification on (https://stackoverflow.com/a/25063574/1484447)
var localdata = [{''}]// Your json array
for (var j = 0; j < localdata.length; j++)
{$(localdata).each(function(index,item)
{
$('#tbl').append('<tr><td>' + item.FirstName +'</td></tr>);
}
The best solution for me was the following:
simple and without using any framework
var doSomethingForAll = function (arg) {
if (arg != undefined && arg.length > 0) {
arg.map(function (item) {
// do something for item
doSomethingForAll (item.subitem)
});
}
}

Javascript, how to split key with dot to recovery json structure

I have a json, it is
{
"prop1.sub1.sub2": "content1",
"prop1.sub1.sub3": "content2",
"prop2.sub1.sub2": "content3",
"prop3.sub1.sub2": "content4"
}
I want to recovery the structure, like
{
"prop1": {
"sub1": {
"sub2" : "content1",
"sub3" : "content2"
}
},
"prop2": {
"sub1": {
"sub2" : "content3"
}
},
"prop3": {
"sub1": {
"sub2" : "content4"
}
}
}
I split the key with dot to get each key.
for (var key in json) {
var keySplit = key.split('.');
// Todo: recovery the structure
}
But not found a good solution.
Is anyone has solution?
You can use Array#reduce method.
var obj = {
"prop1.sub1.sub2": "content1",
"prop1.sub1.sub3": "content2",
"prop2.sub1.sub2": "content3",
"prop3.sub1.sub2": "content4"
};
// iterate over the property names
Object.keys(obj).forEach(function(k) {
// slip the property value based on `.`
var prop = k.split('.');
// get the last value fom array
var last = prop.pop();
// iterate over the remaining array value
// and define the object if not already defined
prop.reduce(function(o, key) {
// define the object if not defined and return
return o[key] = o[key] || {};
// set initial value as object
// and set the property value
}, obj)[last] = obj[k];
// delete the original property from object
delete obj[k];
});
console.log(obj);
Answer by Pranav C Balan is right for the question you asked. But JSON's might not be as simple as you have mentioned above and can have array's also and few keys might not have "." in them. To handle all these cases you can use the following one.
var obj = {
"prop1.sub1.sub2": "content1",
"prop1.sub1.sub3": "content2",
"prop2.sub1.sub2": "content3",
"prop3.0.sub2": "content4"
};
function createJSONStructure(obj) {
Object.keys(obj).forEach(function(k) {
var prop = k.split('.'); //split on . to get elements
if(prop.length >1){ //If there is no dot just key the value as is.
let data = obj;//Copy the default object to data in each loop
for(i=0;i<prop.length-1;i++){
if(data[prop[i]]){ // Check if the key exists
if((prop[i+1].match(/^\d+$/) && !Array.isArray(data[prop[i]])) // Check if the next key is a digit and the object we have is a JSON
|| (!prop[i+1].match(/^\d+$/) && Array.isArray(data[prop[i]]))){ // Check if the next key is not a digit and the object we have is a Array
throw new Error("Invalid header data"); //If any of the above cases satisfy we cannot add the key so we can throw an error.
}
data = data[prop[i]]; // If key exisits make the data variable as the value of the key
}else {
if(prop[i+1].match(/^\d+$/)){ //If the key is not available see if the next parameter is a digit or string to decide if its array or string
data[prop[i]] = [];
}else{
data[prop[i]] = {};
}
data = data[prop[i]]; //Assign this new object to data
}
};
data[prop[i]] = obj[k]; //Finally add the value to final key
delete obj[k]; // delete the exisiting key value
}
});
return obj;
}
console.log(createJSONStructure(obj));

Using recursive function to get data from parent nodes

I have a data structure like the following:
obj
name
parent
name
parent
name
parent
I'm trying to do a recursive function to get the name element for as long as there is a parent element. I've come up with the following code, but it doesn't work because it converts the result to a string (and not an object). Can someone give me some advice on how to best achieve this. The nesting of parent elements is varied, not fixed (even though above I only specified 3 layers). It can range from 1 to 100.
My Desired Result
My end goal is to extract all the 'name' elements from every 'parent' down the hierarchy (and push them to an array).
function getElem(obj){
var result = '';
var parent = '.parent';
var temp = '';
if(!obj.parent){
return obj.name
}
else {
//structure is obj.parent.parent.parent...name
temp += parent;
result = obj + temp + '.name';
console.log(result);
getElem(result);
}
}
getElem(e.data);
function getElem(obj, arr) {
arr = arr || [];
if (obj.name) {
arr.push(obj.name);
}
if (obj.parent) {
return (getElem(obj.parent, arr));
}
else {
return (arr);
}
}
JSFiddle
Assuming that your data structure looks like this
var obj = {
name: 'abc',
parent: {
name: 'def',
parent: {
name: 'ghi',
parent: {
name: 'jkl'
}
}
}
};
function for loop that walks recursively for "parent" key by assigning "parent" key's value in obj and breaks the loop when the key "parent" is not available...
function get_names(obj, key) {
var names = [];
if(key == "undefined") {
key = "parent"; // default value of key
}
do {
if(typeof obj === "undefined") {
break; // breaks the loop when obj/parent is undefined
}
names.push(obj.name); // pushes all the elements named as 'name'
} while(obj = obj.parent);
return names;
}
Logs the array in console
console.log(get_names(obj));
I don't think you need recursion.
function getElem(obj) {
var names = [obj.name];
while (obj.parent) {
obj = obj.parent;
names.push(obj.name);
}
return names;
}

Getting the first index of an object

Consider:
var object = {
foo: {},
bar: {},
baz: {}
}
How would I do this:
var first = object[0];
console.log(first);
Obviously, that doesn’t work because the first index is named foo,
not 0.
console.log(object['foo']);
works, but I don’t know it’s named foo. It could be named anything. I just want the first.
Just for fun this works in JS 1.8.5
var obj = {a: 1, b: 2, c: 3};
Object.keys(obj)[0]; // "a"
This matches the same order that you would see doing
for (o in obj) { ... }
If you want something concise try:
for (first in obj) break;
alert(first);
wrapped as a function:
function first(obj) {
for (var a in obj) return a;
}
they're not really ordered, but you can do:
var first;
for (var i in obj) {
if (obj.hasOwnProperty(i) && typeof(i) !== 'function') {
first = obj[i];
break;
}
}
the .hasOwnProperty() is important to ignore prototyped objects.
This will not give you the first one as javascript objects are unordered, however this is fine in some cases.
myObject[Object.keys(myObject)[0]]
If the order of the objects is significant, you should revise your JSON schema to store the objects in an array:
[
{"name":"foo", ...},
{"name":"bar", ...},
{"name":"baz", ...}
]
or maybe:
[
["foo", {}],
["bar", {}],
["baz", {}]
]
As Ben Alpert points out, properties of Javascript objects are unordered, and your code is broken if you expect them to enumerate in the same order that they are specified in the object literal—there is no "first" property.
for first key of object you can use
console.log(Object.keys(object)[0]);//print key's name
for value
console.log(object[Object.keys(object)[0]]);//print key's value
There is no way to get the first element, seeing as "hashes" (objects) in JavaScript have unordered properties. Your best bet is to store the keys in an array:
var keys = ["foo", "bar", "baz"];
Then use that to get the proper value:
object[keys[0]]
ES6
const [first] = Object.keys(obj)
Using underscore you can use _.pairs to get the first object entry as a key value pair as follows:
_.pairs(obj)[0]
Then the key would be available with a further [0] subscript, the value with [1]
I had the same problem yesterday. I solved it like this:
var obj = {
foo:{},
bar:{},
baz:{}
},
first = null,
key = null;
for (var key in obj) {
first = obj[key];
if(typeof(first) !== 'function') {
break;
}
}
// first is the first enumerated property, and key it's corresponding key.
Not the most elegant solution, and I am pretty sure that it may yield different results in different browsers (i.e. the specs says that enumeration is not required to enumerate the properties in the same order as they were defined). However, I only had a single property in my object so that was a non-issue. I just needed the first key.
You could do something like this:
var object = {
foo:{a:'first'},
bar:{},
baz:{}
}
function getAttributeByIndex(obj, index){
var i = 0;
for (var attr in obj){
if (index === i){
return obj[attr];
}
i++;
}
return null;
}
var first = getAttributeByIndex(object, 0); // returns the value of the
// first (0 index) attribute
// of the object ( {a:'first'} )
To get the first key of your object
const myObject = {
'foo1': { name: 'myNam1' },
'foo2': { name: 'myNam2' }
}
const result = Object.keys(myObject)[0];
// result will return 'foo1'
Based on CMS answer. I don't get the value directly, instead I take the key at its index and use this to get the value:
Object.keyAt = function(obj, index) {
var i = 0;
for (var key in obj) {
if ((index || 0) === i++) return key;
}
};
var obj = {
foo: '1st',
bar: '2nd',
baz: '3rd'
};
var key = Object.keyAt(obj, 1);
var val = obj[key];
console.log(key); // => 'bar'
console.log(val); // => '2nd'
My solution:
Object.prototype.__index = function(index)
{
var i = -1;
for (var key in this)
{
if (this.hasOwnProperty(key) && typeof(this[key])!=='function')
++i;
if (i >= index)
return this[key];
}
return null;
}
aObj = {'jack':3, 'peter':4, '5':'col', 'kk':function(){alert('hell');}, 'till':'ding'};
alert(aObj.__index(4));

Traverse all the Nodes of a JSON Object Tree with JavaScript

I'd like to traverse a JSON object tree, but cannot find any library for that. It doesn't seem difficult but it feels like reinventing the wheel.
In XML there are so many tutorials showing how to traverse an XML tree with DOM :(
If you think jQuery is kind of overkill for such a primitive task, you could do something like that:
//your object
var o = {
foo:"bar",
arr:[1,2,3],
subo: {
foo2:"bar2"
}
};
//called with every property and its value
function process(key,value) {
console.log(key + " : "+value);
}
function traverse(o,func) {
for (var i in o) {
func.apply(this,[i,o[i]]);
if (o[i] !== null && typeof(o[i])=="object") {
//going one step down in the object tree!!
traverse(o[i],func);
}
}
}
//that's all... no magic, no bloated framework
traverse(o,process);
A JSON object is simply a Javascript object. That's actually what JSON stands for: JavaScript Object Notation. So you'd traverse a JSON object however you'd choose to "traverse" a Javascript object in general.
In ES2017 you would do:
Object.entries(jsonObj).forEach(([key, value]) => {
// do something with key and val
});
You can always write a function to recursively descend into the object:
function traverse(jsonObj) {
if( jsonObj !== null && typeof jsonObj == "object" ) {
Object.entries(jsonObj).forEach(([key, value]) => {
// key is either an array index or object key
traverse(value);
});
}
else {
// jsonObj is a number or string
}
}
This should be a good starting point. I highly recommend using modern javascript methods for such things, since they make writing such code much easier.
function traverse(o) {
for (var i in o) {
if (!!o[i] && typeof(o[i])=="object") {
console.log(i, o[i]);
traverse(o[i]);
} else {
console.log(i, o[i]);
}
}
}
There's a new library for traversing JSON data with JavaScript that supports many different use cases.
https://npmjs.org/package/traverse
https://github.com/substack/js-traverse
It works with all kinds of JavaScript objects. It even detects cycles.
It provides the path of each node, too.
Original Simplified Answer
For a newer way to do it if you don't mind dropping IE and mainly supporting more current browsers (check kangax's es6 table for compatibility). You can use es2015 generators for this. I've updated #TheHippo's answer accordingly. Of course if you really want IE support you can use the babel JavaScript transpiler.
// Implementation of Traverse
function* traverse(o, path=[]) {
for (var i in o) {
const itemPath = path.concat(i);
yield [i,o[i],itemPath,o];
if (o[i] !== null && typeof(o[i])=="object") {
//going one step down in the object tree!!
yield* traverse(o[i], itemPath);
}
}
}
// Traverse usage:
//that's all... no magic, no bloated framework
for(var [key, value, path, parent] of traverse({
foo:"bar",
arr:[1,2,3],
subo: {
foo2:"bar2"
}
})) {
// do something here with each key and value
console.log(key, value, path, parent);
}
If you want only own enumerable properties (basically non-prototype chain properties) you can change it to iterate using Object.keys and a for...of loop instead:
function* traverse(o,path=[]) {
for (var i of Object.keys(o)) {
const itemPath = path.concat(i);
yield [i,o[i],itemPath,o];
if (o[i] !== null && typeof(o[i])=="object") {
//going one step down in the object tree!!
yield* traverse(o[i],itemPath);
}
}
}
//that's all... no magic, no bloated framework
for(var [key, value, path, parent] of traverse({
foo:"bar",
arr:[1,2,3],
subo: {
foo2:"bar2"
}
})) {
// do something here with each key and value
console.log(key, value, path, parent);
}
EDIT: This edited answer solves infinite looping traversals.
Stopping Pesky Infinite Object Traversals
This edited answer still provides one of the added benefits of my original answer which allows you to use the provided generator function in order to use a cleaner and simple iterable interface (think using for of loops as in for(var a of b) where b is an iterable and a is an element of the iterable). By using the generator function along with being a simpler api it also helps with code reuse by making it so you don't have to repeat the iteration logic everywhere you want to iterate deeply on an object's properties and it also makes it possible to break out of the loop if you would like to stop iteration earlier.
One thing that I notice that has not been addressed and that isn't in my original answer is that you should be careful traversing arbitrary (i.e. any "random" set of) objects, because JavaScript objects can be self referencing. This creates the opportunity to have infinite looping traversals. Unmodified JSON data however cannot be self referencing, so if you are using this particular subset of JS objects you don't have to worry about infinite looping traversals and you can refer to my original answer or other answers. Here is an example of a non-ending traversal (note it is not a runnable piece of code, because otherwise it would crash your browser tab).
Also in the generator object in my edited example I opted to use Object.keys instead of for in which iterates only non-prototype keys on the object. You can swap this out yourself if you want the prototype keys included. See my original answer section below for both implementations with Object.keys and for in.
Worse - This will infinite loop on self-referential objects:
function* traverse(o, path=[]) {
for (var i of Object.keys(o)) {
const itemPath = path.concat(i);
yield [i,o[i],itemPath, o];
if (o[i] !== null && typeof(o[i])=="object") {
//going one step down in the object tree!!
yield* traverse(o[i], itemPath);
}
}
}
//your object
var o = {
foo:"bar",
arr:[1,2,3],
subo: {
foo2:"bar2"
}
};
// this self-referential property assignment is the only real logical difference
// from the above original example which ends up making this naive traversal
// non-terminating (i.e. it makes it infinite loop)
o.o = o;
//that's all... no magic, no bloated framework
for(var [key, value, path, parent] of traverse(o)) {
// do something here with each key and value
console.log(key, value, path, parent);
}
To save yourself from this you can add a set within a closure, so that when the function is first called it starts to build a memory of the objects it has seen and does not continue iteration once it comes across an already seen object. The below code snippet does that and thus handles infinite looping cases.
Better - This will not infinite loop on self-referential objects:
function* traverse(o) {
const memory = new Set();
function * innerTraversal (o, path=[]) {
if(memory.has(o)) {
// we've seen this object before don't iterate it
return;
}
// add the new object to our memory.
memory.add(o);
for (var i of Object.keys(o)) {
const itemPath = path.concat(i);
yield [i,o[i],itemPath, o];
if (o[i] !== null && typeof(o[i])=="object") {
//going one step down in the object tree!!
yield* innerTraversal(o[i], itemPath);
}
}
}
yield* innerTraversal(o);
}
//your object
var o = {
foo:"bar",
arr:[1,2,3],
subo: {
foo2:"bar2"
}
};
/// this self-referential property assignment is the only real logical difference
// from the above original example which makes more naive traversals
// non-terminating (i.e. it makes it infinite loop)
o.o = o;
console.log(o);
//that's all... no magic, no bloated framework
for(var [key, value, path, parent] of traverse(o)) {
// do something here with each key and value
console.log(key, value, path, parent);
}
EDIT: All above examples in this answer have been edited to include a new path variable yielded from the iterator as per #supersan's request. The path variable is an array of strings where each string in the array represents each key that was accessed to get to the resulting iterated value from the original source object. The path variable can be fed into lodash's get function/method. Or you could write your own version of lodash's get which handles only arrays like so:
function get (object, path) {
return path.reduce((obj, pathItem) => obj ? obj[pathItem] : undefined, object);
}
const example = {a: [1,2,3], b: 4, c: { d: ["foo"] }};
// these paths exist on the object
console.log(get(example, ["a", "0"]));
console.log(get(example, ["c", "d", "0"]));
console.log(get(example, ["b"]));
// these paths do not exist on the object
console.log(get(example, ["e", "f", "g"]));
console.log(get(example, ["b", "f", "g"]));
You could also make a set function like so:
function set (object, path, value) {
const obj = path.slice(0,-1).reduce((obj, pathItem) => obj ? obj[pathItem] : undefined, object)
if(obj && obj[path[path.length - 1]]) {
obj[path[path.length - 1]] = value;
}
return object;
}
const example = {a: [1,2,3], b: 4, c: { d: ["foo"] }};
// these paths exist on the object
console.log(set(example, ["a", "0"], 2));
console.log(set(example, ["c", "d", "0"], "qux"));
console.log(set(example, ["b"], 12));
// these paths do not exist on the object
console.log(set(example, ["e", "f", "g"], false));
console.log(set(example, ["b", "f", "g"], null));
EDIT Sep. 2020: I added a parent for quicker access of the previous object. This could allow you to more quickly build a reverse traverser. Also you could always modify the traversal algorithm to do breadth first search instead of depth first which is actually probably more predictable in fact here's a TypeScript version with Breadth First Search. Since this is a JavaScript question I'll put the JS version here:
var TraverseFilter;
(function (TraverseFilter) {
/** prevents the children from being iterated. */
TraverseFilter["reject"] = "reject";
})(TraverseFilter || (TraverseFilter = {}));
function* traverse(o) {
const memory = new Set();
function* innerTraversal(root) {
const queue = [];
queue.push([root, []]);
while (queue.length > 0) {
const [o, path] = queue.shift();
if (memory.has(o)) {
// we've seen this object before don't iterate it
continue;
}
// add the new object to our memory.
memory.add(o);
for (var i of Object.keys(o)) {
const item = o[i];
const itemPath = path.concat([i]);
const filter = yield [i, item, itemPath, o];
if (filter === TraverseFilter.reject)
continue;
if (item !== null && typeof item === "object") {
//going one step down in the object tree!!
queue.push([item, itemPath]);
}
}
}
}
yield* innerTraversal(o);
}
//your object
var o = {
foo: "bar",
arr: [1, 2, 3],
subo: {
foo2: "bar2"
}
};
/// this self-referential property assignment is the only real logical difference
// from the above original example which makes more naive traversals
// non-terminating (i.e. it makes it infinite loop)
o.o = o;
//that's all... no magic, no bloated framework
for (const [key, value, path, parent] of traverse(o)) {
// do something here with each key and value
console.log(key, value, path, parent);
}
Depends on what you want to do. Here's an example of traversing a JavaScript object tree, printing keys and values as it goes:
function js_traverse(o) {
var type = typeof o
if (type == "object") {
for (var key in o) {
print("key: ", key)
js_traverse(o[key])
}
} else {
print(o)
}
}
js> foobar = {foo: "bar", baz: "quux", zot: [1, 2, 3, {some: "hash"}]}
[object Object]
js> js_traverse(foobar)
key: foo
bar
key: baz
quux
key: zot
key: 0
1
key: 1
2
key: 2
3
key: 3
key: some
hash
If you're traversing an actual JSON string then you can use a reviver function.
function traverse (json, callback) {
JSON.parse(json, function (key, value) {
if (key !== '') {
callback.call(this, key, value)
}
return value
})
}
traverse('{"a":{"b":{"c":{"d":1}},"e":{"f":2}}}', function (key, value) {
console.log(arguments)
})
When traversing an object:
function traverse (obj, callback, trail) {
trail = trail || []
Object.keys(obj).forEach(function (key) {
var value = obj[key]
if (Object.getPrototypeOf(value) === Object.prototype) {
traverse(value, callback, trail.concat(key))
} else {
callback.call(obj, key, value, trail)
}
})
}
traverse({a: {b: {c: {d: 1}}, e: {f: 2}}}, function (key, value, trail) {
console.log(arguments)
})
I wanted to use the perfect solution of #TheHippo in an anonymous function, without use of process and trigger functions. The following worked for me, sharing for novice programmers like myself.
(function traverse(o) {
for (var i in o) {
console.log('key : ' + i + ', value: ' + o[i]);
if (o[i] !== null && typeof(o[i])=="object") {
//going on step down in the object tree!!
traverse(o[i]);
}
}
})
(json);
Most Javascript engines do not optimize tail recursion (this might not be an issue if your JSON isn't deeply nested), but I usually err on the side of caution and do iteration instead, e.g.
function traverse(o, fn) {
const stack = [o]
while (stack.length) {
const obj = stack.shift()
Object.keys(obj).forEach((key) => {
fn(key, obj[key], obj)
if (obj[key] instanceof Object) {
stack.unshift(obj[key])
return
}
})
}
}
const o = {
name: 'Max',
legal: false,
other: {
name: 'Maxwell',
nested: {
legal: true
}
}
}
const fx = (key, value, obj) => console.log(key, value)
traverse(o, fx)
My Script:
op_needed = [];
callback_func = function(val) {
var i, j, len;
results = [];
for (j = 0, len = val.length; j < len; j++) {
i = val[j];
if (i['children'].length !== 0) {
call_func(i['children']);
} else {
op_needed.push(i['rel_path']);
}
}
return op_needed;
};
Input JSON:
[
{
"id": null,
"name": "output",
"asset_type_assoc": [],
"rel_path": "output",
"children": [
{
"id": null,
"name": "output",
"asset_type_assoc": [],
"rel_path": "output/f1",
"children": [
{
"id": null,
"name": "v#",
"asset_type_assoc": [],
"rel_path": "output/f1/ver",
"children": []
}
]
}
]
}
]
Function Call:
callback_func(inp_json);
Output as per my Need:
["output/f1/ver"]
var test = {
depth00: {
depth10: 'string'
, depth11: 11
, depth12: {
depth20:'string'
, depth21:21
}
, depth13: [
{
depth22:'2201'
, depth23:'2301'
}
, {
depth22:'2202'
, depth23:'2302'
}
]
}
,depth01: {
depth10: 'string'
, depth11: 11
, depth12: {
depth20:'string'
, depth21:21
}
, depth13: [
{
depth22:'2201'
, depth23:'2301'
}
, {
depth22:'2202'
, depth23:'2302'
}
]
}
, depth02: 'string'
, dpeth03: 3
};
function traverse(result, obj, preKey) {
if(!obj) return [];
if (typeof obj == 'object') {
for(var key in obj) {
traverse(result, obj[key], (preKey || '') + (preKey ? '[' + key + ']' : key))
}
} else {
result.push({
key: (preKey || '')
, val: obj
});
}
return result;
}
document.getElementById('textarea').value = JSON.stringify(traverse([], test), null, 2);
<textarea style="width:100%;height:600px;" id="textarea"></textarea>
I've created library to traverse and edit deep nested JS objects. Check out API here: https://github.com/dominik791
You can also play with the library interactively using demo app:
https://dominik791.github.io/obj-traverse-demo/
Examples of usage:
You should always have root object which is the first parameter of each method:
var rootObj = {
name: 'rootObject',
children: [
{
'name': 'child1',
children: [ ... ]
},
{
'name': 'child2',
children: [ ... ]
}
]
};
The second parameter is always the name of property that holds nested objects. In above case it would be 'children'.
The third parameter is an object that you use to find object/objects that you want to find/modify/delete. For example if you're looking for object with id equal to 1, then you will pass { id: 1} as the third parameter.
And you can:
findFirst(rootObj, 'children', { id: 1 }) to find first object
with id === 1
findAll(rootObj, 'children', { id: 1 }) to find all objects
with id === 1
findAndDeleteFirst(rootObj, 'children', { id: 1 }) to delete first matching object
findAndDeleteAll(rootObj, 'children', { id: 1 }) to delete all matching objects
replacementObj is used as the last parameter in two last methods:
findAndModifyFirst(rootObj, 'children', { id: 1 }, { id: 2, name: 'newObj'}) to change first found object with id === 1 to the { id: 2, name: 'newObj'}
findAndModifyAll(rootObj, 'children', { id: 1 }, { id: 2, name: 'newObj'}) to change all objects with id === 1 to the { id: 2, name: 'newObj'}
We use object-scan for many data processing tasks. It's powerful once you wrap your head around it. Here is how you could do basic traversal
// const objectScan = require('object-scan');
const obj = { foo: 'bar', arr: [1, 2, 3], subo: { foo2: 'bar2' } };
objectScan(['**'], {
reverse: false,
filterFn: ({ key, value }) => {
console.log(key, value);
}
})(obj);
// => [ 'foo' ] bar
// => [ 'arr', 0 ] 1
// => [ 'arr', 1 ] 2
// => [ 'arr', 2 ] 3
// => [ 'arr' ] [ 1, 2, 3 ]
// => [ 'subo', 'foo2' ] bar2
// => [ 'subo' ] { foo2: 'bar2' }
.as-console-wrapper {max-height: 100% !important; top: 0}
<script src="https://bundle.run/object-scan#13.8.0"></script>
Disclaimer: I'm the author of object-scan
This Will read All Nodes to a map.
function readJsonFile() {
let jsonString = getValueById("testDataContent");
let jsonObj = JSON.parse(jsonString);
let jsonElements = [];
jsonElements = traverse(jsonObj, jsonElements);
console.log(jsonElements)
}
function traverse(jsonObj, jsonElements) {
if (jsonObj !== null && typeof jsonObj == "object") {
Object.entries(jsonObj).forEach(([key, value]) => {
if (typeof value == "object") {
var obj = [];
let map = new Map();
map.set(key, traverse(value, obj))
jsonElements.push(map);
} else {
var obj = [];
obj.key = key;
obj.value = value;
jsonElements.push(obj);
}
});
} else {
}
return jsonElements;
}
You can get all keys / values and preserve the hierarchy with this
// get keys of an object or array
function getkeys(z){
var out=[];
for(var i in z){out.push(i)};
return out;
}
// print all inside an object
function allInternalObjs(data, name) {
name = name || 'data';
return getkeys(data).reduce(function(olist, k){
var v = data[k];
if(typeof v === 'object') { olist.push.apply(olist, allInternalObjs(v, name + '.' + k)); }
else { olist.push(name + '.' + k + ' = ' + v); }
return olist;
}, []);
}
// run with this
allInternalObjs({'a':[{'b':'c'},{'d':{'e':5}}],'f':{'g':'h'}}, 'ob')
This is a modification on (https://stackoverflow.com/a/25063574/1484447)
var localdata = [{''}]// Your json array
for (var j = 0; j < localdata.length; j++)
{$(localdata).each(function(index,item)
{
$('#tbl').append('<tr><td>' + item.FirstName +'</td></tr>);
}
The best solution for me was the following:
simple and without using any framework
var doSomethingForAll = function (arg) {
if (arg != undefined && arg.length > 0) {
arg.map(function (item) {
// do something for item
doSomethingForAll (item.subitem)
});
}
}

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