How does JavaScript compare a number to a string?

Question

I know the meaning of ===: it will check whether the operands are identical or not，so

1 === '1' will give false and
1 == '1' will give true,

But typeof 1 is number and typeof '1' is string, so how is JavaScript comparing 1 == '1'? Are there any conversions happening? If so, which ones?

the standard: http://es5.github.io/#x11.9.3 – georg Sep 27 '13 at 13:57 — georg, Sep 27 '13 at 13:57

idmean · Answer 1 · 2013-09-27T14:07:41.193

4

If types are number and string,

JavaScript will convert the string to a number.

Out of Annotated ECMAScript 5.1:

The comparison x == y, where x and y are values, produces true or false. Such a comparison is performed as follows:

...

5. If Type(x) is Number and Type(y) is String, return the result of the comparison x == ToNumber(y). 6. If Type(x) is String and Type(y) is Number, return the result of the comparison ToNumber(x) == y.

edited Sep 27 '13 at 14:07

answered Sep 27 '13 at 14:02

idmean

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It's not converted with parseInt, ToNumber behaves differently. – bfavaretto Sep 27 '13 at 14:05
@bfavaretto There is no ToNumber in JavaScript – idmean Sep 27 '13 at 14:12
It's an internal operation defined in the specification, it's not exposed to the language. See http://es5.github.io/#x9.3 – bfavaretto Sep 27 '13 at 14:15
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Actually, what I just said isn't correct: it's exposed indirectly via the `Number` constructor http://es5.github.io/#x15.7.1 – bfavaretto Sep 27 '13 at 14:17

Andrew · Answer 2 · 2013-09-27T14:28:06.103

0

You can do 1 == parseInt("1") to parse the string into an integer.

edited Sep 27 '13 at 14:28

answered Sep 27 '13 at 13:56

Andrew

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yes, but if you do not parseint the string, if you just use 1 == '1', it will say true – user2131316 Sep 27 '13 at 13:57
Are you asking if it will say true if you don't do a parseInt? – Andrew Sep 27 '13 at 14:00
Yes, it will be true. It's like PHP where if you did 1 === '1' then it would return false. – Andrew Sep 27 '13 at 14:03
Using a radix of 1? How on earth would that work? The radix needs to be between 2 and 36. – Simon Forsberg Sep 27 '13 at 14:19
@SimonAndréForsberg I'm not familiar with the radix of 1. I did a console.log in firebug with 1 === '1' and it returns false. – Andrew Sep 27 '13 at 14:24
The second parameter to `parseInt` is the radix. `parseInt("1", 1)` is incorrect. – Simon Forsberg Sep 27 '13 at 14:25

score 0 · Answer 3 · answered Sep 27 '13 at 13:59

0

Use String()

It converts the input to a string before doing a comparison.

Example:

var test1= 1;
var test2= "1";

var answer = String(test1) === String(test2);

Answer will equal true in this case.

answered Sep 27 '13 at 13:59

Adam Botley

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yes, but if you only type 1 == '1', it will be true, so how javascript compare it? does javascript will convert the test1 to string automatically? – user2131316 Sep 27 '13 at 14:01
This answers your question a bit better then, I thought you were wanting to know how to convert the values before comparing! http://stackoverflow.com/a/7625195/2509123 – Adam Botley Sep 27 '13 at 14:06

How does JavaScript compare a number to a string?

3 Answers3