how exactly do Javascript numeric comparison operators handle strings?

Question

var i = ['5000','35000'];
alert((i[0] < i[1])?'well duh!':'fuzzy math?');
alert((Number(i[0]) < Number(i[1]))?'well duh!':'fuzzy math?');

What's happening here? In the first alert, the text string "5000" evaluates as not less than "35000". I assumed Javascript used Number() when numerically comparing strings, but apparently that's not the case. Just curious how exactly Javascript handles numerically comparing the strings of numbers by default.

SLaks · Accepted Answer · 2011-11-18 03:07:24Z

4

Javascript compares strings by character value, whether the strings look like numbers or not.

You can see this in the spec, section 11.8.5, point 4.

'a' < 'b' and 'ab' < 'ac are both true.

answered Nov 18, 2011 at 3:07

SLaks

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4 Comments

Wick Over a year ago

Thanks! That point 4(a) string comparison prefix criteria is pretty interesting too.

Wick Over a year ago

Okay I'm still missing something -- I understand your examples above, but I don't understand how the character value of "5000" is not less than the character value of "35000". Can you run me through how the character values are calculated for my specific example?

SLaks Over a year ago

@Wick: "5" is more than "3". This is a purely character-based comparison.

Teemu Over a year ago

The spec link seems to have some new content now (art therapy for drug addictions).

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