JavaScript Code Inside <script> Tag

Question

Apparently a JSON object can be passed inside a linked script. I'm trying to figure out exactly how this works (or if it does):

<script type="text/javascript" src="https://getfirebug.com/firebug-lite.js">
{
    overrideConsole: false,
    startInNewWindow: true,
    startOpened: true,
    enableTrace: true
}
</script>

I noticed it here in the firebug lite documentation: http://getfirebug.com/firebuglite#ScriptJSONOptions

Answer 1

The content is not executed because the element has a src attribute. It's not strictly legal as is. The HTML5 spec says:

If there is a src attribute, the element must be either empty or contain only script documentation that also matches script content restrictions.

The content of that <script> element is neither valid JSON nor valid JavaScript. It is not valid JSON because the property names are not quoted. It is not valid JavaScript because, although it looks like a block expression with labeled statements, the colon after startInNewWindow cannot legally appear there.

That said, the script that is loaded can always look for the last script element and parse its content:

 var scripts = document.getElementsByTagName('SCRIPT');
 var lastScript = scripts[script.length - 1];
 var content = eval(lastScript.innerText || lastScript.textContent);

Answer 2

The browser will ignore any content in <script src /> tag.

However, the Firebug Lite Javascript will specifically find its <script> tag and parse the content manually.

Answer 3

Here is the code in question that parses the JSON object in case anyone is interested.

// process the Script JSON Options
var innerOptions = FBL.trim(script.innerHTML);
if (innerOptions) {
    var innerOptionsObject = eval("(" + innerOptions + ")");

    for (var name in innerOptionsObject) {
        var value = innerOptionsObject[name];

        if (name == "debug") {
            Env.isDebugMode = !!value;
        }
        else if (name in Env.Options) {
            Env.Options[name] = value;
        }
        else {
            Env[name] = value;
        }
    }
}

http://code.google.com/p/fbug/source/browse/lite/branches/firebug1.5/build/firebug-lite-debug.js#478