Writing a custom javascript event

Question

I'm writing some code that will get executed before the DOM loads, basically, using Modernizr to get scripts. Now my issue is that I want to show a loading animation if the DOM loads and the scripts are still loading.

Modernizr is executed in the head. If I put the code to use document.getElementById in the head also, error is thrown because the DOM hasn't loaded. Now I have no idea how to solve this.

Here is the code I have so far:

<head>
 <script>
     var FileManager = {
         IsLoading = false;
         LoadRequiredFiles: function (config) {
             config = config || {};
             this.OnLoading = config.onLoadingCallback;
             this.OnComplete = config.onCompleteCallback;
             this.IsLoading = true;
             if (this.OnLoading) {
                 this.OnLoading();
             }

             var self = this;
             Modernizr.load([{
                 load: '/jquery.min.js',
                 complete: function () {
                         if (self.OnComplete) {
                             self.OnComplete();
                         }
                         self.IsLoading = true;

                 }
             },
            ]);
         }
     };
     var globalLoadingId = 'globalLoader';
     FileManager.LoadRequiredFiles({
         onLoadingCallback: function () {
             document.getElementById(globalLoadingId).style.display = 'block';
         },
         onCompleteCallback: function () {
             document.getElementById(globalLoadingId).style.display = 'none';
         }
     });
</script>

I used to execute this code below the <body> tag, and it worked. Now I moved it into the <head>. So I used to pass 2 callbacks to it. Now I'd rather attach events to it and handle them in the body (assuming thats where the DOM is loaded).

What I'd like to do:

<head>
<script>
    FileManager.LoadRequiredFiles();
</script>
</head>

<body>
<script>

    //Bind the event, not sure if this is even possible in javascript.
    FileManager.OnCompleted += fileManagerCompleted;

    fileManagerCompleted()
    {
         document.getElementById(globalLoadingId).style.display = 'none';
    }

    if(FileManager.IsLoading)
    {
        document.getElementById(globalLoadingId).style.display = 'block';
    }
</script>
</body>

jfriend00 · Accepted Answer · 2011-07-25 02:49:49Z

1

The page is your canvas for display. You can't show anything before it loads. It sounds more like you want a very small page to load (quickly) where you could display your progress and then your code could dynamically load/display the rest of the page with ajax calls and javascript showing progress as it goes. That's the only way to get out in front of the rest of the page load that I know of.

edited Jul 25, 2011 at 2:49

answered Jul 25, 2011 at 2:35

jfriend00

711k104 gold badges1.1k silver badges1k bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

Shawn Mclean Over a year ago

So just load everything below the head? As how I had it before.

jfriend00 Over a year ago

I didn't understand your question. You cannot display anything in the page until it has loaded. You will get the fastest page display if <script> tags are at the end of the <body>.

Jeremy J Starcher · Accepted Answer · 2011-07-25 03:25:35Z

0

The only entirely reliable way to run a script that manipulates the DOM is to use the body onload event. (window.onload is popular, but not quite 100% reliable.)

There are some browsers that implement a onDocumentReady event that can be kind-of-sort-of faked in IE, but I don't recommend its use.

answered Jul 25, 2011 at 3:25

Jeremy J Starcher

24k6 gold badges56 silver badges75 bronze badges

Comments

RobG · Accepted Answer · 2011-07-25 04:06:34Z

Using getElementById will not, by itself, throw an error if used in the head. You might be causing an error because you aren't checking the returned value, which will be null if an element with the specified id wasn't found, e.g.

var el = document.getElementById('foo');

if (el) {
  // do somethig with el
} else {
  // el wasn't found
}

Your problem is how to display the image only if the scripts are still loading and the page is visible. The simple answer is don't use client-side script loading, do it at the server. :-)

If you want to persist with script loading, add a class to the loading image, say "hideOnLoad". Have a callback from the last script load that sets the rule to "display: none" (just create and add style sheet with that one rule using script).

Now you just include the loading image as the first element in the body with a class of "hideOnLoad", knowing that when scripts have finished loading they will hide the image regardless of whether it (or any other element with the same class) existed at the time or not.

Collectives™ on Stack Overflow

Writing a custom javascript event

3 Answers 3

2 Comments

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

2 Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related