Determine if script is loaded

[pman]

I'm trying to add/load a javascript on the document dynamically. This part is okay, but I need to know if the script has been loaded completely or not so that from a 2nd script I can call functions that are on the first script(loading dynamically).

What I have found so far by googling about it, looks like there's no way of doing it. I thought I would ask here in case I missed it. Without modifying the first script, which will be loaded dynamically, is there any way of finding if the script has been completely loaded or not? Does DOM have any properties for this?

Let me know if you have any suggestions. I hope I explained it properly, if not, let me know and I'll try to elaborate it. Thanks

[jscheuer1]

If the first script has any functions and/or variables in it that you are depending upon, just check to see if they are what they need to be before using them.

Say the script has a function:

function reallyImporatant(){
return 'magic things';
}

Before trying to use it, you could always test:

if(typeof reallyImporatant=='function')

[pman]

Thanks so much for your reply jscheuer1. I'll try your suggestions, but I think I'm gonna have to use a for loop or a while loop when checking if it's a function. That might be another problem. From previous experience, I think this will put the browser into an infinite loop and then crash. Anyways, I'll try it out.

Say the script has a function:

Code:

function reallyImporatant(){
return 'magic things';
}

Before trying to use it, you could always test:

Code:

if(typeof reallyImporatant=='function')

Now, let's say the function reallyImportant() is calling another function in the same script like this:

Code:

function reallyImporatant(){
var val = getValue() ;
}

If the script didn't load completely but

if(typeof reallyImporatant=='function')

returns true and I call the function reallyImportant(), it's probably not going to work all the time. Again, I don't know if I was able to explain the problem properly.

[Twey]

Have the script call a callback when it's loaded?

[pman]

Have the script call a callback when it's loaded?

Thanks Twey, But that would require me to modify the script. Also, how would I know when it's loaded? Correct me if I misunderstood your post.

[jscheuer1]

Scripts generally load only one way, or consistently for certain browsers according to what methods they support and how that causes the script to branch. So, all you need to do is to determine what is the last thing to get assigned that's essential to the script's use. A well written script, even if it branches will end up with certain things defined, or at least one out of three, something like that. I'm not going to second guess what that is/these are in a script I haven't seen. If all else fails, it could be determined via trial and error.

Now, I didn't mean to say that what I was offering was a complete solution. I had no way of knowing what you were going to do with that test. One use could be:

function myDependantFunc(){
if(typeof reallyImporatant=='function'){
do dependant stuff here;
}
else
setTimeout("myDependantFunc()",300);
}

You could even count the loops and give up and do something else if - say a minute, or 3 seconds, or whatever passed and what you need from the other script wasn't ready yet.

[pman]

Thanks John and Twey. I think both you have a good solution. As Twey suggested, I could write a call back function in my script and someone else could use that if they are using my script. And if I'm using someone else's script, I guess I could use John's suggestion.

I think now that web 2.0 is really spreading out and api is available from all over the place, may be we should look into dynamically loading javascript. Or else the page will take much longer to load than it should. Also, it probably doesn't make sense to load a whole bunch of javascript files at the beginning and most of it may not be used depending on what the user is doing on the page.

That's why I think loading javascripts (same applies for CSS) dynamically is the best approach and also script functionalities should be separated in different files instead of having everything in the same file, but then I got stuck at the question that I asked in this thread.

Thanks again.

[jscheuer1]

I think the up and coming solution to script loading is third party hosting of popular code libraries. That way, chances are that the user already has most of the code cached.

With today's high speed connections though, you would need to have many, many very complex and long scripts to take much of a loading hit from just them. Images and things like audio, video, and Flash are, and will continue to be the real bandwidth hogs.

Images can be optimized to speed page loading.

[Twey]

But even a single image is usually many thousand times the size of a script. I don't think I've ever seen a 100k+ Javascript file.

[jscheuer1]

But? Don't you mean 'And'?