Javascript onload事件 - 如何判断脚本是否已加载？

Question

如何使用javascript确定HTMLScriptElement是否已完全加载？

如何在不使用onload或onreadystate更改事件的情况下确定动态加载的脚本是否已完成加载？

代码如下:

   TOOL.loadScript = function (url, callback, reappend, deepSearch) {
      var head, curr, child, tempScript, alreadyAppended, queue, 
      alreadyHandled, script, handler, loadFunc; 

      head = document.getElementsByTagName("head")[0];
      tempScript = document.createElement("script");
      tempScript.src = url;
      alreadyAppended = false;

      queue = []; 

      if (deepSearch) {
         // search entire document
         queue.push(document.firstElementChild);
      }
      else { 
         // just search the head element
         queue.push(head); 
      }

      while (queue.length !== 0) { 
         curr = queue.shift();

         // add child nodes to queue
         child = curr.firstElementChild; 
         if (child !== null && child !== undefined) { 
            queue.push(child);
            child = child.nextElementSibling;
            while (child !== null && child !== undefined) { 
               queue.push(child);
               child = child.nextElementSibling;
            } 
         }

         if (curr.tagName !== null && curr.tagName !== undefined) {
            if (curr.tagName.toLowerCase() === "script" && curr.src === tempScript.src) {
               script = curr;
               alreadyAppended = true;
               break;
            }
         }
      }

      if (!alreadyAppended) { 
         script = document.createElement("script");
         script.type = "text/javascript"; 
         script.async = true; 
         script.src = url; 
      } 

      alreadyHandled = false; 

      handler = function (event) {
         console.log("handling event..."); 
         if (!alreadyHandled) { 
            if ((!event.readyState) || (event && (event.readyState === "loaded" || event.readyState === "complete"))) {  
               alreadyHandled = true; 
               callback.apply(script, [url]);
               if (loadFunc) { 
                  loadFunc.apply(script, arguments); 
               }
            }
         }
      }; 

      if (script.onreadystatechange === undefined) { 
         loadFunc = script.onload;
         script.onload = handler; 
      } 
      else { 
         loadFunc = script.onreadystatechange; 
         script.onreadystatechange = handler; 
      } 

我需要帮助.我希望即使alreadyAppeneded === true已经加载了相同的脚本也会触发回调函数,但只有当该脚本完全加载时才会触发.

      if (!alreadyAppended || (alreadyAppended && reappend)) { 
         head.appendChild(script); 
      } 
   };

BOTTOM LINE:如何确定脚本是否已完成加载？如果需要,请问我问题.

谢谢.

Answer 1

惰性实现：创建一个数组，可用于将所有已加载脚本的源推送到其上，并在加载脚本时将其推送到列表中。每次，检查给定的 src 是否在数组中，如果在，则立即触发回调。

当案例被附加但未加​​载时，您如何处理它成为问题。如果您希望回调触发，但希望它在加载后触发，您可以创建一个关联数组，其中 src 作为键，脚本元素作为值。从那里，通过包装原始内容使 onload 或 onreadystatechange 触发两次，如下所示：

var temponload = element.onreadystatechange || element.onload;
if (element.onreadystatechange === undefined)
    element.onload = function(e) { temponload(); temponload(); };
else
    element.onreadystatechange = function (e) { temponload(); temponload(); };

您可能还有其他代码需要连接到此代码，但这应该可以帮助您开始。