JavaScript set anonymous Object key to variable name - Stack Overflow

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    var curr = data[i],
        newArray = [],
        key = curr.Frequency.Type,
        obj = {key: []};
    newArray.push(obj);

However, this yields an object with a key of "key"! How can I create a new object with a key of the value of the variable key?

    var curr = data[i],
        newArray = [],
        key = curr.Frequency.Type,
        obj = {key: []};
    newArray.push(obj);

However, this yields an object with a key of "key"! How can I create a new object with a key of the value of the variable key?

• javascript

Share Improve this question Follow asked Sep 4, 2013 at 15:26 benhowdle89benhowdle89 37.5k7474 gold badges207207 silver badges340340 bronze badges 4

• 2 This is a very frequently asked question. – Pointy Commented Sep 4, 2013 at 15:28
• 1 possible duplicate of Key for javascript dictionary is not stored as value but as variable name – Pointy Commented Sep 4, 2013 at 15:29
• 1 possible duplicate of How to use a variable as a key inside object initialiser – zzzzBov Commented Sep 4, 2013 at 15:30
• Here's one that's even older: stackoverflow./a/15960027/497418 – zzzzBov Commented Sep 4, 2013 at 15:38

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4 Answers 4

Sorted by: Reset to default 2

You can do this:

var curr = data[i],
    newArray = [],
    key = curr.Frequency.Type,
    obj = {};

obj[key] = [];
newArray.push(obj);

There's no way to do it in JavaScript within the object literal itself; the syntax just doesn't provide for that.

edit — when this answer was written, the above was true, but ES2015 provides for dynamic keys in object initializers:

var curr = data[i],
    key = curr.Frequency.Type,
    newArray = [ { [key]: [] } ];

I think you mean this notation:

var type = "some type";
var obj = {}; // can't do it one line
obj[type] = [];
console.log(obj); // { "some type": [] }

simply instantiate a new anonymous object from a function.

obj = new function () {
    this[key] = [];
};

I realise this is an old question but for those finding this through Google the way to do this with ES6+ is to use square bracket notation in the object literal:

const key = 'dynamicKey';
const value = 5;

const objectWithDynamicKey = {
  staticKey: 'another value',
  [key]: value 
}
console.log(objectWithDynamicKey) 

Which prints:

{ 
  staticKey: 'another value', 
  dynamicKey: 5
}

So your example should be:

var curr = data[i];
var newArray = [];
var key = curr.Frequency.Type;
var obj = { [key]: [] };
newArray.push(obj);

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