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我理解在流行的JavaScript库(如jQuery和Prototype)中使用(单个)美元符号.我也理解PHP(变量变量)中双美元符号的重要性.Dean Edwards在他着名的addEvent() JavaScript函数中使用了双美元符号.这是一个包含使用双美元符号的除外:

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" …