Using spread operator to update an object value

Question

I have a function which adds a key to incoming object, but I have been told to use spread operator for that, I have been told that I can use the spread operator to create a new object with the same properties and then set isAvailable on it.

  return new Partner(ServerConfig, capabilities, initialState)
}

class Partner {
  constructor (ServerConfig, capabilities, initialState) {
    initialState.isAvailable = true

So I tried something like this but coulndt succeed, can you help me ? and confused, should I use spread operator in this way , return from a function ?

newObject = {}

// use this inside a function and get value from return

       return {
         value: {
           ...newObject,
           ...initialState
         }
       }

initialState.isAvailable = true

`...` isn't an operator. It's syntax, notation, but not an operator (like the `()` in a `for` statement). — T.J. Crowder, Mar 26 '18 at 12:23
please properly format your code. Ideally, give a standalone example that can be executed. — metakermit, Mar 26 '18 at 12:24

score 136 · Accepted Answer · answered Mar 26 '18 at 12:24

The properties are added in order, so if you want to override existing properties, you need to put them at the end instead of at the beginning:

return {
  value: {
    ...initialState,
    ...newObject
  }
}

You don't need newObject (unless you already have it lying around), though:

return {
  value: {
    ...initialState,
    isAvailable: newValue
  }
}

Example:

const o1 = {a: "original a", b: "original b"};
// Doesn't work:
const o2 = {a: "updated a", ...o1};
console.log(o2);
// Works:
const o3 = {...o1, a: "updated a"};
console.log(o3);

I can't thank you enough. – Muhammad Bilal Feb 06 '22 at 14:34 — Muhammad Bilal, Feb 06 '22 at 14:34

score 27 · Answer 2 · answered Mar 26 '20 at 20:30

If you know the name of the property (a in the example below), then @crowder's answer is perfect:

const o3 = {...o1, a: "updated a"};
console.log(o3);

If the property name is in a variable, then you need to use Computed Property names syntax:

let variable = 'foo'
const o4 = {...o1, [variable]: "updated foo"};
console.log(o4);

Using spread operator to update an object value

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