How does the == operator converts data types in JS?

Question

var number = 2;
var string = '2';
if (number == string){
    return true;
}

The code above will return true. I was wondering how the == operator works. Will it convert the integer to string and then do the comparsion or the oposite?

http://stackoverflow.com/questions/359494/does-it-matter-which-equals-operator-vs-i-use-in-javascript-comparisons — Johnathan Ralls, Apr 18 '15 at 13:15
This has been asked before, [checkout post about type coercion in JS.][1] [1]: http://stackoverflow.com/a/359509/554389 — Ivo, Apr 18 '15 at 13:38

score 0 · Answer 1 · answered Apr 18 '15 at 13:26

0

== operator does change the data type. we can use parseInt in JavaScript for number and toString for string

If we compare like that it always return false :-

var number = parseInt("2");
var string = '2';
var str=string.toString;
if (number == str){
   return TRUE;
}else{
   return FALSE;
}

answered Apr 18 '15 at 13:26

Saty

22,443
7
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Of course that does return `FALSE` (which throws an `undefined variable error`), because you are comparing a function to a number. – Bergi Apr 18 '15 at 14:13

score 0 · Answer 2 · answered Apr 18 '15 at 13:40

0

you must define the base when you use the parseInt function and use the === to compare the strict equality :

var number = parseInt('2', 10);
var string = '2';
return (number === string);

answered Apr 18 '15 at 13:40

Nicolas Pennec

7,533
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Yes. But the OP neither uses `parseInt` nor `===`? – Bergi Apr 18 '15 at 14:11

score 0 · Accepted Answer · answered Apr 18 '15 at 14:10

I was wondering how the == operator works. Will it convert the integer to string and then do the comparison or the opposite?

No, it will convert the string to a number and then do the comparison.

You can read the exact Abstract Equality Algorithm in the spec if you want.

How does the == operator converts data types in JS?

3 Answers3