Wait for a javascript namespace to become available, with timeout!

usage.js

// in this example, we wait for jquery to become available.
waitFor("$",1000*60,function(){
 console.log('jQuery is ready to be used!');
})

waitFor.js

/**
 * A function to wait for a namespace to be available
 * @param {*} namespace the namespace to wait for
 * @param {*} timeout The timout in milliseconds
 * @param {*} callback The callback to perform once the namespace is available
 * @param {*} interval time (in milisecponds) between each call. Default 100.
 */
function waitFor(namespace, timeout, callback, interval) {
    var defaultInterval = interval>=0 ? interval : 100; // try every 100 milliseconds (10 times per second) number chosen to enhance performance;
    if (window[namespace]) { // namespace exists
        callback();
    } else if (timeout <= 0) { // check if we reached the timeout
        return;
    } else {
        setTimeout(function() { // namespace does not exist, wait interval amount then try again;
            waitFor(namespace, timeout - defaultInterval, callback, interval);
        }, defaultInterval);
    }
}