I want an object to call a function defined in another object or JSON (as a string or reference), with a variable number of values also defined there.
Here's a pseudo-code example of what I'm trying to do:
// function name and variable-length values definition
const definition = {
functionName: "function1",
values: [ 1, "foo", 3.14 ]
}
// objectA calling the function with the values
// objectA.definedFunction(definedValues);
// objectA.[functionName]([val1], [val2], ..., [valN]);
objectA.function1(1, "foo", 3.14);
Note: objectA may/should? reference the definition in a member variable.
How can that be achieved?
And is it possible to expand that so that function1 is a member function of another object that is also defined in definition?
There are two mechanisms you need.
First the square bracket notation to access object properties:
objectA[definition.functionName]; // this will return the function you want
// This is the same as objectA.function1
Second you want to pass an array as parameter list. For that you can use Function.prototype.apply which expects the argument list in the form of an array:
objectA[definition.functionName].apply(objectA, definition.values);
// This is the same as objectA.function1(1, "foo", 3.14);
string to function: Function
const fx1 = Function(definition.functionString)
const fx2 = objectA[definition.functionName]
there has serval way to call fx, depend on how fx handle parameter
fx.apply(null, definition.values)
fx(...definition.values)
fx(definition.values)
If you have an object (i.e. dictionary) of functions and their arguments' values, you can get the function simply by accessing its matching value in the dictionary.
Then, in order to use its arguments, you can use the spread operator:
const dictionary = {
function1: { // For example
definition: (a, b, c) => `{ a: ${a}, b: ${b}, c: ${c} }`,
values: [1, "foo", 3.14],
},
};
function callFunctionByName(name) {
const currFunction = dictionary[name];
const { definition, values } = currFunction;
return definition(...values);
}
console.log(callFunctionByName('function1'));
let objA = {
function1: function(a, b, c) {
console.log(a)
console.log(b);
console.log(c);
}
}
const definition = {
functionName: "function1",
values: [ 1, "foo", 3.14 ]
}
objA[definition.functionName].apply(null, definition.values);
//Second approach if it function1 is not a key of objA
function function1(first, sec, third) {
console.log(first);
console.log(sec);
console.log(third);
}
const definition = {
functionName: "function1",
values: [ 1, "foo", 3.14 ]
}
eval(`${definition.functionName}(${definition.values[0]}, "${definition.values[1]}", ${definition.values[2]})`);
Today I came across the following syntax which I didn't recognize:
const createUser = ({
age = 1,
name = 'Anonymous',
}) => ({
age,
name,
});
const defaultP = createUser({
age: 5
});
console.log(defaultP);
I think it uses Object destructuring and default parameters in order to set defaults of the object which is send as an argument.
The syntax threw me a bit off because normally I see object destructuring only in the following manner:
let obj = {
prop1: 1
}
const {prop1} = obj;
console.log(prop1);
Question:
How does this syntax work exactly?
That syntax indeed uses Object Destructuring in order to extract default values from the parameter object. There are some examples in the Mozilla documentation that helps us understand the trick, check this out:
var {a = 10, b = 5} = {a: 3};
console.log(a); // 3
console.log(b); // 5
A possible disadvantage of your example is that the createUser method ignores all other values of the parameter object and always returns an object that contains only age and name. If you want to make this more flexible, we could use Object.assign() like this:
const createUser = (o) => Object.assign({ age: 1, name: 'Anonymous' }, o);
In this case, the user created will be an object that merges the parameter object with the default values. Note now that the default values are in the method body. With this method we can create users that contain other properties, example:
const superman = createUser({ name: 'Superman', type: 'superhero' });
console.log(superman);
// output: {age: 1, name: "Superman", type: "Superhero"}
Your code is using both Object Destructuring and default function props.
const createUser = ({
age = 1,
name = 'Anonymous',
}) => ({
age,
name,
});
Here function createUser is accepting single argument of type Object. Function is returing same object, if you have both object properties defined in your argument, then it will return your passed object. Otherwise it will replace it with default values, which are 1 and Anonymous respectively.
You can further read about it here:
https://wesbos.com/destructuring-renaming/
https://wesbos.com/destructuring-default-values/
If you use babel and transpile your code to ES5, it will look like this:
function createUser(params) {
return {
age: typeof params.age === 'undefined' ? 1 : params.age,
name: typeof params.name === 'undefined' ? 'Anonymous' : params.name,
};
}
Just a note: default values for function arguments works the same way:
const multiply = (a, optionalB) => {
const b = typeof optionalB !== 'undefined' ? optionalB : 2;
return a * b;
}
Is same as:
const multiply = (a, b = 2) => {
return a * b;
}
It increases a readability, mostly in cases when argument is used several times.
In React Redux, Reducers state change needs to copy values of only specific keys. How do i do that using spread syntax.
const initialState = {
Information: {
Manufacturer: undefined,
Model: undefined
}
};
My structure is as above. I get a response from REST as below:
{
"#odata.context": "/redfish/v1/$metadata#ComputerSystem.ComputerSystem",
"#odata.id": "/redfish/v1/Systems/1/",
"Bios":{
"#odata.id": "/redfish/v1/systems/1/bios/"
"Manufacturer": "ABC"
}
How do i extract value of only Manufacturer.
If you have a code example, I could give a better answer, but here's a shot:
function getSpecificKeys (input) {
const { foo, bar, baz, ...other } = input
return { foo, bar, baz } // to return only foo, bar baz
// or, return every other key/value
// return other
}
Update
This is what I understood from your comment.
// You have a data structure like this:
const info = { a: undefined, b: undefined }
// You want to write a function that updates info with payload
// where payload looks like this
const payload = {
model: { a: "a value" },
date: { b: "b value" }
}
// therefore the function should look like this
function mergePayload (info, payload) {
const { model: { a }, date: { b } } = payload
return { ...info, a, b }
// NOTE that this will return a new object and not modify info reference
// if you want to MODIFY info, then do this:
// info.a = a
// info.b = b
}
i have two javascript object with the next syntax:
let section = { name: "foo", tables: [] }
let field = { name: "bar", properties: {} }
and a function who expect those objects, but in the function i only use the name of each object, so i wanted to know if i can destructuring the two objects in the function's declaration like:
function something( {name}, {name} ) {
//code
}
the first should be section.name and the second should be field.name.
Is there a way two do a destructuring in this scenario? or should i spect only the names in the function?
Which is better?
Thank you.
Yup, it looks like you can label/reassign the parameters: {before<colon>after}
var section = { name: 'foo', tables: [] };
var field = { name: "bar", properties: {} };
function something({ name: sectionName }, { name: fieldName }) {
console.log(sectionName, fieldName);
}
something(section, field);
What's a good and short way to remove a value from an object at a specific key without mutating the original object?
I'd like to do something like:
let o = {firstname: 'Jane', lastname: 'Doe'};
let o2 = doSomething(o, 'lastname');
console.log(o.lastname); // 'Doe'
console.log(o2.lastname); // undefined
I know there are a lot of immutability libraries for such tasks, but I'd like to get away without a library. But to do this, a requirement would be to have an easy and short way that can be used throughout the code, without abstracting the method away as a utility function.
E.g. for adding a value I do the following:
let o2 = {...o1, age: 31};
This is quite short, easy to remember and doesn't need a utility function.
Is there something like this for removing a value? ES6 is very welcome.
Thank you very much!
Update:
You could remove a property from an object with a tricky Destructuring assignment:
const doSomething = (obj, prop) => {
let {[prop]: omit, ...res} = obj
return res
}
Though, if property name you want to remove is static, then you could remove it with a simple one-liner:
let {lastname, ...o2} = o
The easiest way is simply to Or you could clone your object before mutating it:
const doSomething = (obj, prop) => {
let res = Object.assign({}, obj)
delete res[prop]
return res
}
Alternatively you could use omit function from lodash utility library:
let o2 = _.omit(o, 'lastname')
It's available as a part of lodash package, or as a standalone lodash.omit package.
With ES7 object destructuring:
const myObject = {
a: 1,
b: 2,
c: 3
};
const { a, ...noA } = myObject;
console.log(noA); // => { b: 2, c: 3 }
one line solution
const removeKey = (key, {[key]: _, ...rest}) => rest;
Explanations:
This is a generic arrow function to remove a specific key. The first argument is the name of the key to remove, the second is the object from where you want to remove the key. Note that by restructuring it, we generate the curated result, then return it.
Example:
let example = {
first:"frefrze",
second:"gergerge",
third: "gfgfg"
}
console.log(removeKey('third', example))
/*
Object {
first: "frefrze",
second: "gergerge"
}
*/
To add some spice bringing in Performance. Check this thread bellow
https://github.com/googleapis/google-api-nodejs-client/issues/375
The use of the delete operator has performance negative effects for
the V8 hidden classes pattern. In general it's recommended do not use
it.
Alternatively, to remove object own enumerable properties, we could
create a new object copy without those properties (example using
lodash):
_.omit(o, 'prop', 'prop2')
Or even define the property value to null or undefined (which is
implicitly ignored when serializing to JSON):
o.prop = undefined
You can use too the destructing way
const {remov1, remov2, ...new} = old;
old = new;
And a more practical exmple:
this._volumes[this._minCandle] = undefined;
{
const {[this._minCandle]: remove, ...rest} = this._volumes;
this._volumes = rest;
}
As you can see you can use [somePropsVarForDynamicName]: scopeVarName syntax for dynamic names. And you can put all in brackets (new block) so the rest will be garbage collected after it.
Here a test:
exec:
Or we can go with some function like
function deleteProps(obj, props) {
if (!Array.isArray(props)) props = [props];
return Object.keys(obj).reduce((newObj, prop) => {
if (!props.includes(prop)) {
newObj[prop] = obj[prop];
}
return newObj;
}, {});
}
for typescript
function deleteProps(obj: Object, props: string[]) {
if (!Array.isArray(props)) props = [props];
return Object.keys(obj).reduce((newObj, prop) => {
if (!props.includes(prop)) {
newObj[prop] = obj[prop];
}
return newObj;
}, {});
}
Usage:
let a = {propH: 'hi', propB: 'bye', propO: 'ok'};
a = deleteProps(a, 'propB');
// or
a = deleteProps(a, ['propB', 'propO']);
This way a new object is created. And the fast property of the object is kept. Which can be important or matter. If the mapping and the object will be accessed many many times.
Also associating undefined can be a good way to go with. When you can afford it. And for the keys you can too check the value. For instance to get all the active keys you do something like:
const allActiveKeys = Object.keys(myObj).filter(k => myObj[k] !== undefined);
//or
const allActiveKeys = Object.keys(myObj).filter(k => myObj[k]); // if any false evaluated value is to be stripped.
Undefined is not suited though for big list. Or development over time with many props to come in. As the memory usage will keep growing and will never get cleaned. So it depend on the usage. And just creating a new object seem to be the good way.
Then the Premature optimization is the root of all evil will kick in. So you need to be aware of the trade off. And what is needed and what's not.
Note about _.omit() from lodash
It's removed from version 5. You can't find it in the repo. And here an issue that talk about it.
https://github.com/lodash/lodash/issues/2930
v8
You can check this which is a good reading https://v8.dev/blog/fast-properties
As suggested in the comments above if you want to extend this to remove more than one item from your object I like to use filter. and reduce
eg
const o = {
"firstname": "Jane",
"lastname": "Doe",
"middlename": "Kate",
"age": 23,
"_id": "599ad9f8ebe5183011f70835",
"index": 0,
"guid": "1dbb6a4e-f82d-4e32-bb4c-15ed783c70ca",
"isActive": true,
"balance": "$1,510.89",
"picture": "http://placehold.it/32x32",
"eyeColor": "green",
"registered": "2014-08-17T09:21:18 -10:00",
"tags": [
"consequat",
"ut",
"qui",
"nulla",
"do",
"sunt",
"anim"
]
};
const removeItems = ['balance', 'picture', 'tags']
console.log(formatObj(o, removeItems))
function formatObj(obj, removeItems) {
return {
...Object.keys(obj)
.filter(item => !isInArray(item, removeItems))
.reduce((newObj, item) => {
return {
...newObj, [item]: obj[item]
}
}, {})
}
}
function isInArray(value, array) {
return array.indexOf(value) > -1;
}
My issue with the accepted answer, from an ESLint rule standard, if you try to destructure:
const { notNeeded, alsoNotNeeded, ...rest } = { ...ogObject };
the 2 new variables, notNeeded and alsoNotNeeded may throw a warning or error depending on your setup since they are now unused. So why create new vars if unused?
I think you need to use the delete function truly.
export function deleteKeyFromObject(obj, key) {
return Object.fromEntries(Object.entries(obj).filter(el => el[0] !== key))
}
with lodash cloneDeep and delete
(note: lodash clone can be used instead for shallow objects)
const obj = {a: 1, b: 2, c: 3}
const unwantedKey = 'a'
const _ = require('lodash')
const objCopy = _.cloneDeep(obj)
delete objCopy[unwantedKey]
// objCopy = {b: 2, c: 3}
For my code I wanted a short version for the return value of map() but the multiline/mutli operations solutions were "ugly". The key feature is the old void(0) which resolve to undefined.
let o2 = {...o, age: 31, lastname: void(0)};
The property stays in the object:
console.log(o2) // {firstname: "Jane", lastname: undefined, age: 31}
but the transmit framework kills it for me (b.c. stringify):
console.log(JSON.stringify(o2)) // {"firstname":"Jane","age":31}
I wrote big function about issue for me. The function clear all values of props (not itself, only value), arrays etc. as multidimensional.
NOTE: The function clear elements in arrays and arrays become an empty array. Maybe this case can be added to function as optional.
https://gist.github.com/semihkeskindev/d979b169e4ee157503a76b06573ae868
function clearAllValues(data, byTypeOf = false) {
let clearValuesTypeOf = {
boolean: false,
number: 0,
string: '',
}
// clears array if data is array
if (Array.isArray(data)) {
data = [];
} else if (typeof data === 'object' && data !== null) {
// loops object if data is object
Object.keys(data).forEach((key, index) => {
// clears array if property value is array
if (Array.isArray(data[key])) {
data[key] = [];
} else if (typeof data[key] === 'object' && data !== null) {
data[key] = this.clearAllValues(data[key], byTypeOf);
} else {
// clears value by typeof value if second parameter is true
if (byTypeOf) {
data[key] = clearValuesTypeOf[typeof data[key]];
} else {
// value changes as null if second parameter is false
data[key] = null;
}
}
});
} else {
if (byTypeOf) {
data = clearValuesTypeOf[typeof data];
} else {
data = null;
}
}
return data;
}
Here is an example that clear all values without delete props
let object = {
name: 'Semih',
lastname: 'Keskin',
brothers: [
{
name: 'Melih Kayra',
age: 9,
}
],
sisters: [],
hobbies: {
cycling: true,
listeningMusic: true,
running: false,
}
}
console.log(object);
// output before changed: {"name":"Semih","lastname":"Keskin","brothers":[{"name":"Melih Kayra","age":9}],"sisters":[],"hobbies":{"cycling":true,"listeningMusic":true,"running":false}}
let clearObject = clearAllValues(object);
console.log(clearObject);
// output after changed: {"name":null,"lastname":null,"brothers":[],"sisters":[],"hobbies":{"cycling":null,"listeningMusic":null,"running":null}}
let clearObject2 = clearAllValues(object);
console.log(clearObject2);
// output after changed by typeof: {"name":"","lastname":"","brothers":[],"sisters":[],"hobbies":{"cycling":false,"listeningMusic":false,"running":false}}