Should a Javascript library dynamically add dependencies?

Question

I'm working on a small JS library that requires jQuery and Raphael. I've documented this fact in the README, but I don't love the idea that users have to manually include three JS libs to use this.

What are the pros and cons of having the library dynamically include the dependencies if it doesn't find them? Like so:

if (!window.jQuery) {
    var _my_script=document.createElement('SCRIPT');
    _my_script.type='text/javascript';
    _my_script.src='//ajax.googleapis.com/ajax/libs/jquery/1.9.1/jquery.min.js?';
    document.getElementsByTagName('head')[0].appendChild(_my_script);
    console.log("Loaded jQuery");        
} else {
    console.log("jQuery already loaded");
}

// get Raphael if not found
if (typeof(Raphael) === "undefined") {
    var _my_script=document.createElement('SCRIPT');
    _my_script.type='text/javascript';
    _my_script.src='//cdnjs.cloudflare.com/ajax/libs/raphael/2.1.0/raphael-min.js?';
    document.getElementsByTagName('head')[0].appendChild(_my_script);
    console.log("Loaded Raphael");        
} else {
    console.log("Raphael already loaded");
}

Kosher?

Claudio Redi · Accepted Answer · 2013-02-18 16:25:54Z

1

I personally don't know any js library that automatically download "external" dependencies and I don't think it's a good idea in a normal case.

Expressing clearly required libraries and minimal versions should be enough and that's how all js libraries I know work.

Libraries like jQuery can be downloaded from CDN, locally, etc so forcing a source and version for everyone would make no sense.

edited Feb 18, 2013 at 16:25

answered Feb 18, 2013 at 16:20

Claudio Redi

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1 Comment

Chris Wilson Over a year ago

Thanks! Bold solid answers.

user1637281 · Accepted Answer · 2013-02-18 16:21:29Z

1

I know that highly popular libraries like backbone.js do not do this.

I think it is better to force the user to do this, so they understand how the library is working.

In general, there is usually some sort of resource loader available, that will handle adding resources. If you do this separately it kind of splinters a grouping of functionality that hopefully the end user is using.

answered Feb 18, 2013 at 16:21

user1637281

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