Comparing negative numbers in JQuery function

Question

I am trying to compare two negative numbers and the comparison is failing. In this specific case, getLeftPercent() is a negative number (-14) yet when comparing, action B is performed. Logically, (-14) is less than (-10) thus action A should be performed.

If I change the right side comparison operand (-10) to a positive number (1 for example) then action A is performed. Is there some quirk of JavaScript that I'm overlooking (which is staring me in the face)? I can post the complete code but there's not really much more.

$(function() {

    // the statement in question
    if (parseInt(getLeftPercent(), 10) < -10) {
        // do action A
        // this is just a debug statement
        $('#posbanner').html('element position is less than negative 10');
    } else {
        // do action B
        // this is just a debug statement
        $('#posbanner').html('element position is greater than  or equal to negative 10');
    }
});

//  element left position on page
function getLeftPercent() {
    var leftStr = $('#sidebar').css('left'),
        pxPos = leftStr.indexOf('px'),
        leftVal = leftStr.substr(0, pxPos),
        leftPercent = (leftVal / $(window).width() * 100).toString(),
        dotPos = leftPercent.indexOf('.'),
        leftPercentStr = dotPos == -1 ? leftPercent  : leftPercent.substr(0, dotPos);
    return leftPercentStr;
};

What is the actual string value returned by getLeftPercent() ? — Comfortably Numb
– Comfortably Numb, Commented Aug 20, 2013 at 17:53
add console.log(getLeftPercent()) and check the result in your console (Ctrl+Shift+J in Chrome/Firefox) — omma2289
– omma2289, Commented Aug 20, 2013 at 17:54
get firebug for FF and debug it step by step, should be able to spot the issue easily — Huangism
– Huangism, Commented Aug 20, 2013 at 17:55
The actual value returned by getLeftPercent() is a number, which is -14. I've tried debugging with no answer. — Jonathan Eggert
– Jonathan Eggert, Commented Aug 20, 2013 at 19:06

Shamim Hafiz - MSFT · Accepted Answer · 2013-08-20 17:55:10Z

2

I tried running the following code on jsfiddle

if (parseInt( -14, 10) < -10)
{
alert("I am in A");
}
else
{
alert("I am in B");
}

I get I am in A Not sure, if getLeftPercent() is returning the value you expect.

answered Aug 20, 2013 at 17:55

Shamim Hafiz - MSFT

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1 Comment

Jonathan Eggert Over a year ago

Thanks for your response. The reason for the $('#posbanner').html ~ statement is to display the actual value returned by getLeftPercent(). It is returning a valid number, but for some reason is not being compared properly

rink.attendant.6 · Accepted Answer · 2013-08-20 17:56:01Z

0

Your getLeftPercent() function seems way overcomplicated. I'm not sure whether your "left" is relative to the document or parent element, I'll assume document here.

function getLeftPercent() {
    'use strict';
    return ( ($('#sidebar').offset()).left * 100 / $(window).width() );
}

answered Aug 20, 2013 at 17:56

rink.attendant.6

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1 Comment

Jonathan Eggert Over a year ago

Yes, the function was something that I borrowed from elsewhere. It is a little more than needed but there were other parts that I removed (functionality was more than just returning percentage.

Comfortably Numb · Accepted Answer · 2013-08-20 18:00:29Z

-1

Most likely your substrings return some characters before the number.

alert(parseInt('-14abc', 10)); // -14

alert(parseInt('abc-14', 10)); // NaN

answered Aug 20, 2013 at 18:00

Comfortably Numb

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2 Comments

Huangism Over a year ago

The string used in the substring is from $('#sidebar').css('left'), I don't think it would include other extra characters

Jonathan Eggert Over a year ago

The value returned by the function is a number and it does match the positioning of the element on the web page. Thanks

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