Javascript compare

Today I found something in Javascript that just doesn’t make any sense. Ok, maybe some other things don’t make sense either, but I think this one just beats all of them.

Let’s say we have a string and a number:

a = "1";
b = 1;

Now we want to compare these:

alert((a>b) ' : ' (aa) ' : ' (b==a));

Both will give you ‘false : false : true’.

If we change a to “2” 

a = "2";
b = 1;

we get a ‘true : false : false’. We’re still OK.

Now let’s change a to “a”

a = "a";
b = 1;

The weird thing is we get ‘false : false : false’ on both alerts.

In typestrict languages you’d get an error. Or at least you should. In php you get a ‘false : true : false’ and ‘true : false : false’ which would mean they decided that all strings are smaller than numbers. This is weird – if you make b a string “1” the return values change – but at least they made a choice.

For what I can comprehend Javascript casts both values to int and I can understand that. The core of the problem is obviously with the NaN value. What I can’t understand is how something’s not smaller, not bigger and not equal at the same time? I’m sure someone can explain this…

This entry was posted on Thursday, May 18th, 2006 at 10:04 and is filed under javascript, technology. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.

3 Responses to “Javascript compare”

  1. Marko says:
    May 19th, 2006 at 08:40

    Is a dream bigger than an apple?

    That’s how :)

  2. Marko Mrdjenovic says:
    May 19th, 2006 at 10:21

    I could accept that in typestrict languages. And I would even accept it here, but how come then 

    var a = ['a',1];
alert(a.sort().join());
var b = [1,'a'];
alert(b.sort().join());

    both return ‘1, a’. Doesn’t this mean that it decides that 1 is smaller than ‘a’ ?

  3. Marko says:
    May 19th, 2006 at 02:04

    I don’t know, it might. But my point is that if you go comparing uncomparable items, then you can reasonable expect undetermined result.

Leave a Reply