dealing with missing properties on nested object while destructring - javascript

I need to destructure a nested object. what is the best way to avoid exceptions when some of the nested properties are missing, while assigning those who do exist?
const data = {
title: 'hello',
// nest: {
// road: 5
// }
};
const { title, nest: { road = '' } } = data;
console.log(road);
/** i want it to return '' or undefined.
* actually it returns: Cannot match against 'undefined' or 'null'
*
*/
console.log(title)
/** i want it to return 'hello'
* actually: never got there as there was an exception.
*/

You can assign in a parent object level to empty object (or with value) even if it has further nested object destruction:
const { title, nest: { road = '<default road>' } = {} } = data;
const data = {
title: 'hello',
//nest: {
// road: 5
//}
};
const { title, nest: { road = '<default road>' } = {} } = data;
console.log(title);
console.log(road);
And also, you are doing it wrong, if you are destructing using
{title: englishTitle} = {title: 1234}
then, you should use englishTitle to get the value 1234, and not title, or use
{title} = {title: 1234}
and use title to get 1234

Related

destructuring nested level of array of object

I have an object where one property contains array of objects, I need to destructure it, but when destructuring I don't know how to handle if that property is of empty array
const dataTest1 = {
id: 1,
details: [{f_name_1: "John"}]
}
const {details : [{f_name_1}] = [{}]} = dataTest1 || {}
console.log(f_name_1 ?? 'NA')
const dataTest2 = {
id: 2
}
const {details : [{f_name_2}] = [{}]} = dataTest2 || {}
console.log(f_name_2 ?? 'NA')
const dataTest3 = {
id: 3,
details: []
}
const {details : [{f_name_3}] = [{}]} = dataTest3 || {}
console.log(f_name_3 ?? 'NA')
If you see the first and second case gives me value or fallback value, but when I pass details as an empty array its going error (dataTest3), because I am destructuring first position of array [{}], how can I give a default value as empty object
You need an object ad default value for the inner object, because you add only an array if the array is missing, but if exist, you have no object.
const dataTest3 = {
id: 3,
details: []
}
const { details: [{ f_name_3 } = {}] = [] } = dataTest3 || {};
console.log(f_name_3 ?? 'NA');

Setting the property of one specific key in an object in a reduce is setting it for all properties

Okay, I have literally no idea whats going on here. I'm assuming its some kind of reference issue? But I dont know how to get around it or whats causing it.
To sum it up, I have a list of objects, as well as an object that gets prepopulated to make sure I have data for all keys in the object.
I need to iterate over this list of objects, and by using the timeframeId in the metadata object, and the id in the data object, I want to assign the entire data object to the corresponding timeframeId and id hierarchy in the prepopulated object.
For some reason, all data properties are being overwritten to whatever the last row data is.
I've linked a repl so you can see for yourself: https://repl.it/#ThomasVermeers1/UnwrittenNoisyFirm#index.js
But my code is as follows:
const buildSegmentsFromRows = (rows, timeframeMetadata, defaultSegmentData) => {
// Prepopulate object to make sure every timeframe has a 'hello' key in it with some data
const emptySegments = timeframeMetadata.reduce((segmentMap, metadata) => {
segmentMap[metadata.timeframeId] = {
metadata,
segments: defaultSegmentData,
};
return segmentMap;
}, {});
// Now simply just loop over the rows, and set [row.metadata.timeframeId].segments[row.data.id] to row.data
const segments = rows.reduce((partialSegments, row) => {
const { timeframeId } = row.metadata;
const { id } = row.data;
/**
* This is the line where everything goes wrong
*/
partialSegments[timeframeId].segments[id] = row.data;
return partialSegments;
}, emptySegments);
return segments;
};
const rows = [
{
metadata: { timeframeId: '20202_01' },
data: {
'id': 'hello', 'value': 15
}
},
{
metadata: { timeframeId: '20202_02' },
data: {
'id': 'hello', 'value': 10
}
}
]
const timeframemetadata = [
{ timeframeId: '20202_01'},
{ timeframeId: '20202_02'}
]
const defaultSegmentData = {
'hello': {
'id': 'hello',
}
}
console.log(JSON.stringify(buildSegmentsFromRows(rows, timeframemetadata, defaultSegmentData), null, 2))
I'm expecting the end result to be:
{
"20202_01": {
"metadata": {
"timeframeId": "20202_01"
},
"segments": {
"hello": {
"id": "hello",
"value": 15
}
}
},
"20202_02": {
"metadata": {
"timeframeId": "20202_02"
},
"segments": {
"hello": {
"id": "hello",
"value": 10
}
}
}
}
But instead, value is getting set to 10 in all instances. I'm thinking its because we're setting the property to row.data, which is a reference, and gets updated on every call? But I'm at a complete loss here.
The problem is that you are referring to the same object for every segments in the list.
Therefore, changing the value of segments[id] will update defaultSegmentData, causing every reference to defaultSegmentData to change as well.
const emptySegments = timeframeMetadata.reduce((segmentMap, metadata) => {
segmentMap[metadata.timeframeId] = {
metadata,
segments: defaultSegmentData, // Everything goes wrong here.
};
return segmentMap;
}, {});
A simple solution to this problem is to avoid using the same reference to the object when creating the segmentMap:
const emptySegments = timeframeMetadata.reduce((segmentMap, metadata) => {
segmentMap[metadata.timeframeId] = {
metadata,
/** Or whatever default value you want.
* Just make sure to create a new instance of it for each call.
*/
segments: {},
};
return segmentMap;
}, {});

How can you destructure an array of objects in Javascript into two predefined variables in ES6?

I have an array containing one object of this form :
Array = [ { type: type, message: message } ]
I keep getting ESLint errors asking me to use object destructuring and array destructuring.
Currently my code looks like this :
let type=null;
let message=null;
if (data.length > 0) {
({ type, message } = data[0]);
}
So far this works and my variables are assigned correctly, however I am still getting the "Use array destructuring" message from ESLint.
Any help with this would be appreciated. Thank you
You can destructure the array:
let type=null;
let message=null;
if (data.length > 0) {
[{ type, message }] = data;
}
The code above is a shorter version of:
[ firstElement ] = data; // array destructruring
({ type, message } = firstElement); // object destructuring
Faly's way is good. You can also use default values when destructuring:
function test(label, data) {
// 1 -----------------------------vvvvv
let [{type = null, message = null} = {}] = data;
// 2 -----^^^^^^^---------^^^^^^^
console.log(label, type, message);
}
test("test1: ", []);
test("test2: ", [{type: "t"}]);
test("test3: ", [{type: "t", message: "m"}]);
That works because if data.length is 0, data[0] is undefined, and so triggers use of the default value {} (1) for the array part of that; within the object part of that, we use null (2) to handle any missing values on the object as well.
EsLint wants you to write
let type = null;
let message = null;
if (data.length > 0) {
[{ type, message }] = data;
}
which destructures the first item of an iterable data into the {type, message} target. (More items are ignored).
I would however recommend to use default values for the empty case:
const [{type, message} = {type:null, message:null}] = data;
or also
const [{type = null, message = null} = {}] = data;

How to get proprety value of object from parent object

I have object in this structure:
obj = {
user: { name: 'jeterson' },
title: 'I am a test'
}
I have one key with value: user.name.
I have trying get value like this: obj[key], meaning obj['user.name']. It not works, only works for obj.title.
My object have many values that are also objects, and i want get value like this:
myobject[mykey]
It is possible get value from property object like above ?
You can access it with:
obj['user']['name']
Or alternatively:
obj.user.name
If you want to get from a key like "user.name" to the value, you woulr have to do some logic yourself. You could hack something together like this:
let obj = {
user: {
name: 'jeterson'
},
title: 'I am a test'
}
let key = 'user.name';
let keys = key.split('.');
let res = obj;
while (keys.length > 0 && res) {
let k = keys.shift();
res = res[k];
}
console.log(res) // "jeterson"
When the keys do not match, res holds undefined.
You've got multiple solutions to access an element of an object with its keys:
var obj = {
user: { name: 'jeterson' },
title: 'I am a test'
}
console.log(obj['user']['name']);
console.log(obj['user'].name);
console.log(obj.user['name']);
console.log(obj.user.name);
But you can't do it easily with a variable key = 'user.name'.
If you need to use a variable containing the nested-keys, you could create a function.
Updated answer: An amazingly short way to achieve it is to use .reduce():
// My function
function obj_tree_key(obj, path) {
return path.split('.').reduce((accu, val) => accu[val] || 'Not found', obj);
}
var obj1 = {
user: {
name: 'jeterson'
},
title: 'I am a test'
}
console.log(obj_tree_key(obj1, 'user.name')); // Outputs "jeterson"
// Here is an example with error:
var obj2 = {
user: {
nameeeee: 'jeterson'
},
title: 'I am a test'
}
console.log(obj_tree_key(obj2, 'user.name'));
Old answer: Use a for to loop through the keys and reduce the oject:
// My function
function obj_tree_key(obj, tree_key) {
var result = obj;
var keys = tree_key.split('.');
for (var i = 0; i < keys.length; i++) {
result = result[keys[i]] || 'Not found'; // Error handling
}
return result;
}
var obj1 = {
user: {
name: 'jeterson'
},
title: 'I am a test'
}
console.log(obj_tree_key(obj1, 'user.name')); // Outputs "jeterson"
// Here is an example with error:
var obj2 = {
user: {
nameeeee: 'jeterson'
},
title: 'I am a test'
}
console.log(obj_tree_key(obj2, 'user.name'));
Hope it helps.
first get the user, then the name:
obj['user']['name']
or
obj.user.name
You can also use
obj.user.name
You could access it using
console.log(obj.user.name);
You can do it in 2 way:
obj['user']['name']
or
obj.user.name

Destructing a javascript object to get inner object

I'm using the following code to get object from react state.
const { organizations } = this.state;
The sate object is as following.
this.state = {
userOrganizations: {},
OrganizationUsers: {}
}
userOrganizations is actually an object with an inner object named organizations. How can I map this using es6 code?
Edit
What I actually need is to get inner objects of both the userOrganizations and OrganizationUsers using the following code.
const { organizations, users } = this.state;
The organizations and users are sub objects which are inside the userOrganizations and OrganizationUsers.
So when I want to handle them, will they work with just calling
const { organizations, users } = this.state.userOrganizations, this.state.OrganizationUsers;
You can nest destructruring like
const { userOrganizations : { organizations } } = this.state;
or simply write
const { organizations } = this.state.userOrganizations;
This is so simple but still many got it wrong. Here is an example of inner destructuring
const obj = {
someArray: [ 1, 2, 3],
someInnerObj : {num: 123, txt: 'text'}
}
const {someArray: [first,second], someInnerObj: { num: myNum, txt: meText}} = obj
console.log(first,second,myNum,meText)
Try it in console
Just use dot notation until you get to the parent object just above the property you want
const obj = { outer: { inner: 'value' }};
const { inner } = obj.outer;
console.log(inner);
To destructure more than one thing at a time in different nested levels, try something like:
const x = {
state: {
userOrganizations: {
organizations: 'orgValue'
},
OrganizationUsers: {
users: 'userValue'
}
}
}
const { userOrganizations: { organizations }, OrganizationUsers: { users } } = x.state;
console.log(organizations + ' ' + users);
If i'am not wrong this should solve your issue,
const { organizations } = this.state.userOrganizations;

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