Question

So I’m working on a site, and we need to check if jQuery is defined before writing it to the page. I want to convert it to use JS conditional shorthand, but for some reason when I do that the statement does not execute. Here is my code:

Original (this works, tested):

if (typeof jQuery == 'undefined') {
    document.write('<script type="text/javascript" src="', JSPATH_REL_symc + 'jquery-1.4.2.min.js','"><\/script>');
}

That version works perfectly. Now I replaced it with this, and for some reason I’m having issues:

New w/Shorthand:

(typeof jQuery == 'undefined') ? document.write('<script type="text/javascript" src="', JSPATH_REL_symc + 'jquery-1.4.2.min.js','"><\/script>') : '';

Any idea what is wrong with this syntax?

Thanks.

Answer 1

Nothing appears to be wrong with it at first glance. (The var JSPATH_REL_symc is defined elsewhere, yes?). The code is a little funky (mixing string concatenation and multiple arguments to document.write — document.write(str, str2 + str3, str4)), but that is easily fixed. Also you ought to be able to simplify (and shorten) the code even further:

this.jQuery || document.write('<script src="'
                              + JSPATH_REL_symc
                              + 'jquery-1.4.2.min.js"><\/script>');

The type attribute of the script tag isn’t mandatory, all browsers will implicitly evaluate its contents or the linked file as JavaScript.

A quick test shows this code in action: http://jsfiddle.net/ZWQqM/ (minus the JSPATH argument, and adding in an “onload” event attribute to the script tag to demonstrate that it is successful.)