JavaScript how to catch event when lazy loaded script is ready? - Stack Overflow

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I have a lazy loading JavaScript file, how can I catch the event when the class in the file is ready for usage? I only need to load this script in a specific case. Therefor it is not loaded via onload but in a if clause.

The lazy loading code I took from here: /

if (externalClassRequired) {
    var s   = document.createElement('script');
    s.type  = 'text/javascript';
    s.async = true;
    s.src   = '.js';
    var x   = document.getElementsByTagName('script')[0]
    x.parentNode.insertBefore(s, x);

    // When do I know when the class named "geo" is available?
}

---

Update:
Sorry guys, I totally forgot about Ajax! :) I was so focused on my problem that I didn't saw the obviously solution by @Tokimon. The simplest solution via jQuery would then be:

$.getScript('.js', function() {
  // callback or use the class directly
});

I have a lazy loading JavaScript file, how can I catch the event when the class in the file is ready for usage? I only need to load this script in a specific case. Therefor it is not loaded via onload but in a if clause.

The lazy loading code I took from here: http://friendlybit./js/lazy-loading-asyncronous-javascript/

if (externalClassRequired) {
    var s   = document.createElement('script');
    s.type  = 'text/javascript';
    s.async = true;
    s.src   = 'http://yourdomain./script.js';
    var x   = document.getElementsByTagName('script')[0]
    x.parentNode.insertBefore(s, x);

    // When do I know when the class named "geo" is available?
}

---

Update:
Sorry guys, I totally forgot about Ajax! :) I was so focused on my problem that I didn't saw the obviously solution by @Tokimon. The simplest solution via jQuery would then be:

$.getScript('http://yourdomain./script.js', function() {
  // callback or use the class directly
});

• javascript
• events

Share Improve this question Follow edited Mar 19, 2011 at 14:03 powtac asked Mar 18, 2011 at 15:48 powtacpowtac 41.1k2828 gold badges118118 silver badges172172 bronze badges

Add a ment  | 

5 Answers 5

Sorted by: Reset to default 3

if (s.readyState) s.onreadystatechange = function () {
    if (s.readyState === "loaded" || s.readyState === "plete") {
        s.onreadystatechange = null;
        callback();
    }
}; else s.onload = function () {
    callback();
};

Or you could get the script via ajax. Then you are sure that the script is loaded when the ajax succes event is fired :)

If I understand what you want to acplish correctly. This is why callback methods exist.

Explained pretty well here Getting a better understanding of callback functions in JavaScript

As it requires a HTTP request, you should be able to put an onload event on it.

s.onload = function() {
  // do something
}

In 'Even Faster Web Sites' Steve Souders offer a solution, which can be seen here.

var onloadCallback = function() {
    alert('onload');
}

var s   = document.createElement('script');
s.type  = 'text/javascript';
s.async = true;
s.onreadystatechange = function () { // for IE
  if (this.readyState == 'plete') onloadCallback();
};
s.onload = onloadCallback; // for other browsers
s.src   = 'http://yourdomain./script.js';
var x   = document.getElementsByTagName('script')[0]
x.parentNode.insertBefore(s, x);   

You could also use an XMLHttpRequest to load the file.

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