I just learned a new trick from my new colleague Adrian. When reviewing some of his code, I stumbled across this little function:

function bind(fnc, val) {
    return function () {
        return fnc(val);
    };
}

What it does, is nothing more than building a closure. Something you could do manually using an anonymous function anyway.

However by introducing the additional wrapping function call it solves a problem very well described by Menno van Slooten. The problem is basically that variables are passed by reference to closures which will hurt you when a variable is reused inside a loop¹⁾.

Van Slooten presented his own solution, but Adrian's simple function turns this:

oListItem.onclick = function(value) {
    return function() {
        alert(value);
    }
}(i);

into this²⁾:

oListItem.onclick = bind(alert,i);

Much nicer, isn't it?

But what if you need to pass more than one argument to your function? Adrian came up with this:

function fix (fnc) {
    var args = Array.prototype.slice.call(arguments, 1);
    return function() {
        return fnc.apply(this, args);
    }
}

Yes. Magic. Advanced magic .

The function grabs all function arguments from the arguments object³⁾ and turns it into an array (skipping the function name itself). It then does what the simpler bind() did above – it executes the function and passes the arguments.

This function will spare me a few headaches in the future for sure and will be added to the DokuWiki script library of course.