How to push into an array of object using the spread operator to a specific element

Question

I have an array as such

const arr = [a={} , b={}]

Now I know the spread operator is not for mutation or pushing but it is very easy to do so with.

I want this button to add elements to a when it's pressed

 <Button
title= {this.props.title}
 onPress={ this.roomNumberPressed }
 />

so the end results be something like :

arr = [a={1,2,3} , b={3,4,5}]

Note: `...` isn't, and can't be, an operator, neither when used for spread nor rest. It does things operators cannot do. [Details](https://stackoverflow.com/questions/44934828/is-foo-an-operator-or-syntax/44934830#44934830). — T.J. Crowder, Sep 17 '18 at 08:22
`const arr = [a={} , b={}]` isn't valid syntax. Do you have an array, or an object with `a` and `b` properties? — T.J. Crowder, Sep 17 '18 at 08:24

score 17 · Accepted Answer · answered Sep 17 '18 at 08:24

I want this button to add elements to a when it's pressed

As you said in your question, spread notation isn't for adding to existing objects. Your options are:

Use spread to create a new object and assign that new object to a:
```
a = {...a, ...theNewPropertiesToAdd};
```
Use Object.assign to add new properties to the existing a:
```
Object.assign(a, theNewPropertiesToAdd);
```

Note I've just used a above because your const arr = [a={}, b={}] is a syntax error, and I can't tell whether you mean const arr = [{}, {}] (in which case a above is arr[0]), or const arr = {a: {}, b: {}} (in which case a above is arr.a [and arr isn't an array]).

@Kuchi - You don't "append" things to variables. You assign them. — T.J. Crowder, Oct 08 '19 at 08:18

How to push into an array of object using the spread operator to a specific element

1 Answers1