jQuery / javascript variable in if statement not working

Question

I have a variable as such:

var is_last = $('.paging a:last').attr('rel');

this returns '-400' which is correct.

However, i need to add 200 to this so the answer is '-200'

if i do this:

var is_last = $('.paging a:last').attr('rel')+200;

the variable is now '-400200'

How can i pass the variable as a value?

A.

Nick Craver · Accepted Answer · 2010-11-13 10:47:44Z

7

You need to parse the output of .attr(), it to an integer first using parseInt() so you're dealing with a number (and not a string), like this:

var is_last = parseInt($('.paging a:last').attr('rel'), 10) + 200;

answered Nov 13, 2010 at 10:47

Nick Craver

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Comments

amelvin · Accepted Answer · 2010-11-13 11:04:12Z

0

I reckon that @Nick Craver is correct and that parseInt is the more correct answer, but as a quick-and-dirty alternative you can also convince javascript that a variable is a number and not a string by multiplying by 1:

    var x = parseInt("-400", 10) + 200;
    var y = ("-400" * 1) + 200;

    alert(x);
    alert(y);

answered Nov 13, 2010 at 11:04

amelvin

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2 Comments

Nick Craver Over a year ago

You can do this, but it's much slower, you can test it here, +"-400" would be the operator shortcut with decent performance here :)

amelvin Over a year ago

Very good comparison tool, the marked improvement in js performance on Chrome 8 compared to Chrome 7 suggests that I should upgrade immediately. Also it is odd how the 6 different techniques would result in markedly different performance in different browsers or versions of browsers - on my Chrome 7 setup, parseInt is the slowest on those benchmarks. Thanks again I will use this reference in conversations!

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