Question

I am attempting to perform mathematical operations with JavaScript on values obtained from an attribute. The attribute is created via a PHP loop. I will give an example of one of the html tags containing the attributes, but keep in mind that there are many of these tags which contain unique attribute values.

The HTML:

<a href="secondary_imgs.php..." mwidth="593"></a>

The JavaScript(jQuery):

    $("a[href^='secondary_imgs.php']").click(function(){
        var pageWidth = $(window).width();
        var maxshadowWidth = (Math.floor(pageWidth * 0.91808874)) - 2;
        var mWidth = $(this).attr("mwidth");
        var maxSecondaryWidth = mWidth + 60;
        alert (maxSecondaryWidth);
        if(maxSecondaryWidth <= maxshadowWidth) {
            var shadowWidth = maxSecondaryWidth;
        } else {
            var shadowWidth = maxshadowWidth;
        }
        var shadowboxrel = 'shadowbox;width=' + shadowWidth;
        $(this).attr('rel', shadowboxrel);

The operation doesn’t seem to be working, and I have a feeling it has to do with my lack of experience using mathematical operations in javascript. In this case, I think something is wrong with my method of using the attribute value, in the mathematical operation.

For example, the above width attribute is defined as 593. I define the maxSecondaryWidth as mWidth + 60. I fired an alert to see what value I was getting. It should have been shown as 653, yet the value that is ‘alerted’ is 59360. Obviously I don’t understand how to add, as the + is concatenating the two values, as opposed to adding them together. Could it have to do with needing to transform the attribute value from a string into an integer?

Answer 1

You have to convert to a number using parseInt(), otherwise + will do string concatenation:

var mWidth = parseInt($(this).attr("mwidth"), 10);

If the attribute can also be a float, use parseFloat() instead of parseInt().