magnetiq.com

I came across yet another browser discrepancy with a rather obscure scenario: A function declaration within a with block:

var obj = { a: 1 };

with (obj) {
    function foo() {
        return typeof a;
    }
}

alert(foo()); // alerts "number" on Firefox, "undefined" on others

This exposes the object properties to the function scope only on Firefox. On all other browsers that I’ve tested with (IE, Safari, Opera and Chrome), the property isn’t visible inside the function.

I’ve been working on extracting some text out of a given JavaScript function when I realized that toString() may return parts of the original comments, depending on the browser. I’ve done a quick test to capture the behaviour of popular browsers. Here’s my test script:

function/*post-keyword*/fn/*post-name*/()/*post-parens*/{
    /*inside*/
}

document.write(fn.toString());

And here are the results I got on different browsers:

And out of the browser context:

While looking for the best solution to extract the parts that I need, I’ve implemented a workaround. Sort of. If blocking the problem can be considered a workaround:

var functionToStringHasComments = /PROBE/.test(function () {/*PROBE*/});

// ...

if (functionToStringHasComments) {
    throw "...";
}