JavaScript Double Dollar Sign

Question

I understand the use of the (single) dollar sign in popular JavaScript libraries such as jQuery and Prototype. I also understand the significance of the double dollar sign in PHP (variable variables). Dean Edwards uses the double dollar sign in his famous addEvent() JavaScript function. Here is an except containing the use of the double dollar sign:

function addEvent(element, type, handler) {   // assign each event handler a unique ID   if (!handler.$$guid) handler.$$guid = addEvent.guid++;   // create a hash table of event types for the element   if (!element.events) element.events = {};   // create a hash table of event handlers for each element/event pair   var handlers = element.events[type];   if (!handlers) {     handlers = element.events[type] = {};     // store the existing event handler (if there is one)     if (element["on" + type]) {       handlers[0] = element["on" + type];     }   }   // store the event handler in the hash table   handlers[handler.$$guid] = handler;   // assign a global event handler to do all the work   element["on" + type] = handleEvent; }; // a counter used to create unique IDs addEvent.guid = 1; 

From what I've read, the dollar sign only officially has significance in JavaScript for code generation tools, although that standard is largely ignored today due to the dollar signs widespread usage in the aforementioned JavaScript libraries.

Can anyone shed any light on this usage of the double dollar sign in JavaScript?

Thanks very much!

Answer 1

I wrote this function. :)

There is no longer any special significance to the $$ prefixes. It was a notation that I used back when packer was popular. Packer would shorten variable names with this prefix. Nowadays Packer will automatically shorten variable names so this notation is redundant.

Short answer, the $ sign is a valid identifier in JavaScript so you are just looking at a bunch of ugly variable names. ;)