How to name the variable with the value of another variable? JS

Question

Is there a way to call a variable based on the value of another variable, which is not always the same?

Example:

var color = 'black';
var [color] = 'whatever'; // the variable name here would be 'black'

Reason for usage: In the reducer of Redux I receive an action that holds a particular value

export default (state = INITIAL_STATE, action) => {
const { size, color, object } = action;
switch (action.type) {
    case (DO_SOMETHING): {
    // instead of name 'output' below, I want to have a value of 'color' 
        let output = object;
        if (size) { 
            output = callExternalFunction(output, size);
        }
        return { ...state, [color]: output };
    }

My goal: If it is possible to do, I will be able to turn the return into this:

return { ...state, [color] };

score 0 · Answer 1 · answered Sep 21 '17 at 09:23

0

Why not just use an object to hold your variables names? For instance :

var color = 'black',
    variables = {};

variables[color] = 'whatever'; // { black : 'whatever' }

return { ...state, variables['black'] } // { ...state, 'whatever' }

Does that fit your needs? Maybe I misunderstood the question

answered Sep 21 '17 at 09:23

Jeremy Thille

26,047
12
43
63

The whole and only purpose of this struggle is merely to condense the size of the code by a few characters. And your solution does not achieve that. – Eduard Sep 21 '17 at 09:32
Oh, so your code works, but you just wanted to make it shorter? I didn't get your point then. – Jeremy Thille Sep 21 '17 at 09:44
I was not specific enough in the post :) – Eduard Sep 21 '17 at 09:57
In the return statement how do you know variables['black'] the value name is "black".You have hardcoded it. – pritesh Sep 21 '17 at 10:04
1

It should return variables[color] – pritesh Sep 21 '17 at 10:08

Fuross · Answer 2 · 2017-09-21T10:05:20.937

0

You can use window object for that. Try this:

var color = 'black';
window[color] = 'whatever';
alert(black);

Edit:

As @Tavish Aggarwal mentioned this will make the variable global, if you really don't want that you could use eval() instead.

But eval is evil, as the saying goes, so I don't recommend it.

edited Sep 21 '17 at 10:05

answered Sep 21 '17 at 09:35

Fuross

488
6
12

Seems to work, but is it a reasonable and practical way of doing for the sake of mere condensation of the code? – Eduard Sep 21 '17 at 09:37
2

@Eduard attaching variable to window is not a good practice. As it makes it a global variable. – Tavish Aggarwal Sep 21 '17 at 09:40
@TavishAggarwal I see, probably should just leave the code in a way it is now. Thanks! – Eduard Sep 21 '17 at 09:42
I thought about using `window`, but I wanted to avoid using a global variable. That's why I suggested using a local object instead of `window`. – Jeremy Thille Sep 21 '17 at 09:43
Yes, but code suggested by you is not what @Eduard want. – Tavish Aggarwal Sep 21 '17 at 09:45
@Eduard I upadated the code for another solution, however I don't think using globals is such a bad thing, as long as you "control" you code. – Fuross Sep 21 '17 at 09:51

How to name the variable with the value of another variable? JS

2 Answers2