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. — T.J. Crowder
– T.J. Crowder, Commented Sep 17, 2018 at 8:22
const arr = [a={} , b={}] isn't valid syntax. Do you have an array, or an object with a and b properties? — T.J. Crowder
– T.J. Crowder, Commented Sep 17, 2018 at 8:24

T.J. Crowder · Accepted Answer · 2018-09-17 08:24:43Z

17

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]).

answered Sep 17, 2018 at 8:24

T.J. Crowder

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1 Comment

T.J. Crowder Over a year ago

@Kuchi - You don't "append" things to variables. You assign them.

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