Question

In my website http://www.theprinterdepo.com, you can view the page source, I have a code that my seo consulting suggested me to move to an external file.

Its an ecommerce site built on magento. ITs a free open source tool, so I did not developed it, I just installed it.

I need to know what the code does.

window.HDUSeed='c7025284683262a8eb81056c48968d74';
window.HDUSeedIntId = setInterval(function(){
    if (document.observe) {
        document.observe('dom:loaded', function(){
            for (var i = 0; i < document.forms.length; i++) {
                if (document.forms[i].getAttribute('action') &&  document.forms[i].getAttribute('action').match('contacts/index/post')) {
                    var el = document.createElement('input');
                    el.type = ('hidden');
                    el.name = 'hdu_seed';
                    el.value = window.HDUSeed;
                    document.forms[i].appendChild(el);
                }
            }
        });
        clearInterval(window.HDUSeedIntId)
    }
}, 100);

Answer 1

In Brief

This script calls a function at an interval of every 100ms or so (as it’s not guaranteed) to try to verify for the DOM’s load status to add a hook on it.

If loaded, it then processes all the forms present in the page, looking for one with an “action” attribute (usually to submit it someplace, here contacts/index/post).

To all such forms found, it adds a new hidden input element containing “seed” value, but we cannot tell you what it is used for without knowing more about the codebase.

Detailed Code Review

// seed value, purpose unknown
window.HDUSeed='c7025284683262a8eb81056c48968d74';

// invoke this function every 100ms
//   see: https://developer.mozilla.org/en/DOM/window.setInterval
window.HDUSeedIntId = setInterval(function(){
    // checks if document.observe method exists (added by the Prototype
    // JavaScript library, so we use this here to check its presence or
    // that it's been already loaded)
    if (document.observe) {
        // hook on load status (when the page's DOM has finished loading)
        //   see: http://www.prototypejs.org/api/document/observe
        document.observe('dom:loaded', function(){
            // process all forms contained within the page's context
            //   see: https://developer.mozilla.org/en/DOM/document.forms
            for (var i = 0; i < document.forms.length; i++) {
                // only act on forms with the 'contacts/index/post/' action attribute
                //   see: https://developer.mozilla.org/en/DOM/document.forms
                //   and: https://developer.mozilla.org/en/JavaScript/Reference/Global_Objects/String/match
                if (document.forms[i].getAttribute('action') && 
                    document.forms[i].getAttribute('action').match('contacts/index/post')) {
                    // create an element...
                    //   see: https://developer.mozilla.org/en/DOM/document.createElement
                    var el = document.createElement('input');
                    el.type = ('hidden');              // ... that is hidden
                    el.name = 'hdu_seed';              // w/ name 'hdu_seed'
                    el.value = window.HDUSeed;         // and the seed value
                    document.forms[i].appendChild(el); // and add it to the end of the form
                }
            }
        });
        // Remove the interval to not call this stub again,
        // as you've done what you want.
        // To do this, you call clearInterval with the ID of the
        // interval callback you created earlier.
        //   see: https://developer.mozilla.org/en/DOM/window.clearInterval
        clearInterval(window.HDUSeedIntId)
    }
}, 100); // 100ms