Enum object as dictionary key

Question

I want to use a so called "enum" object as dictionary key,(actually,it is also a dictionary AFAIK), in JavaScript.

This doesn't work:

    var State ={DEFAULT:0,ACTIVE:1 ,INACTIVE:2,ALERT:3};

    var statesDict =  {
      State.ACTIVE : {color:0x00ff00}
      State.INACTIVE: {color:0x000000}
    };

while this one does:

   var State ={DEFAULT:0,ACTIVE:1 ,INACTIVE:2,ALERT:3};

    var statesDict =  {
      1: {color:0x00ff00}
      2: {color:0x000000}
    };

Why? Isn't the State.{prop name} supposed to be replaced by its value?

`var statesDict = { [State.ACTIVE]: {color:0x00ff00}, ... }`. You can't do substitution for property name variables without the brackets. — Heretic Monkey, May 20 '18 at 17:54
@RokoC.Buljan No, you can create property names without the quotes for object literals... — Heretic Monkey, May 20 '18 at 17:57
Quick note: You can only use strings as dictionary keys and anything else, except for [Symbols](https://developer.mozilla.org/en-US/docs/Glossary/Symbol), will be converted via the `toString` function. — schroffl, May 20 '18 at 17:58
@RokoC.Buljan I prefer keeping things which are not string as not strings )) — Michael IV, May 20 '18 at 17:58

score 15 · Accepted Answer · answered May 20 '18 at 17:56

15

You could use computed property names with brackets.

var State = { DEFAULT: 0, ACTIVE: 1, INACTIVE: 2, ALERT: 3 },
    statesDict = {
        [State.ACTIVE]: { color: 0x00ff00 },
        [State.INACTIVE]: { color: 0x000000 }
    };

console.log(statesDict);

answered May 20 '18 at 17:56

Nina Scholz

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Based on the output I see the key is a string now. Is it the way Js works with types? I can't keep keys as integers? Or "types" have no meaning in Js? )) – Michael IV May 20 '18 at 18:00
You can. Here you are trying to evaluate some expression to a Number. Generally yes, Numbers can be keys. (they will be converted to strings) – Attersson May 20 '18 at 18:02
1

all keys of objects, even indices of arrays are strings. – Nina Scholz May 20 '18 at 18:02
@NinaScholz Great,thanks for the clarification. Js is weird language. – Michael IV May 20 '18 at 18:04
1

@MichaelIV: JS now has a [`Symbol`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Symbol) type, which would be better here if ES6 can be used. They don't get converted to strings when used as object properties. `{ DEFAULT: Symbol(), ACTIVE: Symbol(), INACTIVE: Symbol(), ALERT: Symbol() }` It also has a `Map` type, which can be used for your `statesDict`, so you could do `statesDict.get(State.ACTIVE))` – May 20 '18 at 18:16

Enum object as dictionary key

1 Answers1