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

Answer 1

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);

Answer 2

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);