Get product ID from class name eg 'productID_123'

I have added a class to a list of product images eg 'productID_123', I would like to get the number from the end. I need this to be as dynamic as possible the image may have more than one class. This is what I have put together so far, I think I am nearly there just can't figure out the IF:

$(".image").each(function(){

    var classList = $(this).attr('class').split(/\s+/);

    $.each( classList, function(i开发者_如何学Cndex, item){
        if (item === 'productID_') {
            product_id = item.replace("productID_","");
            fetchProductImages(product_id,this.width,this.height);
        }
    });

});

Maybe can I enforce that it is an integer that is returned?

I can't use the data-* attribute because the page is written in XHTML Strict and is required to validate.

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You could use a regular expression:

$.each( classList, function(index, item){
    var matched = item.match( /^productID_(\d+)$/ );
    if (matched) {
        var product_id = matched[1];
        fetchProductImages(product_id,this.width,this.height);
    }
});