JavaScript that executes after page load

2018-12-31 01:32发布

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I'm executing an external script, using a <script> inside <head>.

Now since the script executes before the page has loaded, I can't access the <body>, among other things. I'd like to execute some JavaScript after the document has been "loaded" (HTML fully downloaded and in-RAM). Are there any events that I can hook onto when my script executes, that will get triggered on page load?

22条回答
浅入江南
2楼-- · 2018-12-31 02:10

Best method, recommended by Google also. :)

<script type="text/javascript">
  function downloadJSAtOnload() {
   var element = document.createElement("script");
   element.src = "defer.js";
   document.body.appendChild(element);
  }
  if (window.addEventListener)
   window.addEventListener("load", downloadJSAtOnload, false);
  else if (window.attachEvent)
   window.attachEvent("onload", downloadJSAtOnload);
  else window.onload = downloadJSAtOnload;
</script>

http://www.feedthebot.com/pagespeed/defer-loading-javascript.html

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怪性笑人.
3楼-- · 2018-12-31 02:10

Using the YUI library (I love it):

YAHOO.util.Event.onDOMReady(function(){
    //your code
});

Portable and beautiful! However, if you don't use YUI for other stuff (see its doc) I would say that it's not worth to use it.

N.B. : to use this code you need to import 2 scripts

<script type="text/javascript" src="http://yui.yahooapis.com/2.7.0/build/yahoo/yahoo-min.js" ></script>
<script type="text/javascript" src="http://yui.yahooapis.com/2.7.0/build/event/event-min.js" ></script>
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素衣白纱
4楼-- · 2018-12-31 02:11

Here's a script based on deferred js loading after the page is loaded,

<script type="text/javascript">
  function downloadJSAtOnload() {
      var element = document.createElement("script");
      element.src = "deferredfunctions.js";
      document.body.appendChild(element);
  }

  if (window.addEventListener)
      window.addEventListener("load", downloadJSAtOnload, false);
  else if (window.attachEvent)
      window.attachEvent("onload", downloadJSAtOnload);
  else window.onload = downloadJSAtOnload;
</script>

Where do I place this?

Paste code in your HTML just before the </body> tag (near the bottom of your HTML file).

What does it do?

This code says wait for the entire document to load, then load the external file deferredfunctions.js.

Here's an example of the above code - Defer Rendering of JS

I wrote this based on defered loading of javascript pagespeed google concept and also sourced from this article Defer loading javascript

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零度萤火
5楼-- · 2018-12-31 02:12

There is a very good documentation on How to detect if document has loaded using Javascript or Jquery.

Using the native Javascript this can be achieved

if (document.readyState === "complete") {
 init();
 }

This can also be done inside the interval

var interval = setInterval(function() {
    if(document.readyState === 'complete') {
        clearInterval(interval);
        init();
    }    
}, 100);

Eg By Mozilla

switch (document.readyState) {
  case "loading":
    // The document is still loading.
    break;
  case "interactive":
    // The document has finished loading. We can now access the DOM elements.
    var span = document.createElement("span");
    span.textContent = "A <span> element.";
    document.body.appendChild(span);
    break;
  case "complete":
    // The page is fully loaded.
    console.log("Page is loaded completely");
    break;
}

Using Jquery To check only if DOM is ready

// A $( document ).ready() block.
$( document ).ready(function() {
    console.log( "ready!" );
});

To check if all resources are loaded use window.load

 $( window ).load(function() {
        console.log( "window loaded" );
    });
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