How to convert a number into a string and use it as an array key in Javascript?

Question

I'm trying to convert a number to a string to use as a key. But the problem is, when I the newly converted string, it still acts like a number. Is there a right way of doing this?

JAVASCRIPT

var arr = [];

var num = 3;

var key = String(''+num); //Convert number into string

//var key = ''  +num;         //Tried this
//var key = num.toString(); //Tried this also

array[key] = true;

console.log(arr); //Returns [, , true]
console.log(arr.length); //Returns 3

Basically, I want it to return just:

console.log(arr); //Return [true]
console.log(arr.length); //Return 1

JavaScript turns any expression you use with the [ ] operator into a string. You don't have to do anything at all. arr[3] is the same as arr["3"]. — Pointy
– Pointy, Commented Jan 28, 2017 at 16:55
@tery.blargh OK well the answer is you cannot do that. You could use a plain object instead of an array however. — Pointy
– Pointy, Commented Jan 28, 2017 at 16:56
I'm not sure what you want to achieve, but arrays don't have "keys", probably you want to use and Object instead? — lucavgobbi
– lucavgobbi, Commented Jan 28, 2017 at 16:56

ibrahim mahrir · Accepted Answer · 2017-01-28 16:57:27Z

3

What you're looking for is an Object ({}) not an Array ([]). Use this instead:

var obj = {};
var key = 3;
obj[key] = true; // no need to convert the key to string

EXAMPLE:

var obj = {};
var key = 3;
obj[key] = true;

console.log(obj);

answered Jan 28, 2017 at 16:57

ibrahim mahrir

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2 Comments

Nina Scholz Over a year ago

so you are looking for an object, instead of an array. plain object have no (built in) length property.

tery.blargh Over a year ago

They do after Object.keys() :)

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