Watch for async loaded remote scripts

watcher-loader.js

/*
 * This is a function that watches global variable
 * Used to track asynchronously loaded remote scripts that do not have 'onload' callbacks
 * When variable is created, callback {name}AsyncInit will be called
 * And this 'watcher' will be replaced by real object
 *
 * Usage:
 *      window.somelibAsyncInit = function(somelib){...}
 *      window.__loadAsync('somelib')
 *
 * Based on ideas of 'watch' polyfill https://gist.github.com/eligrey/384583
 */
 
window.__loadAsync = function(name) {
    
    if (typeof name !== 'string') { throw 'Invalid object name!' }
    
    // Defining names for temp variable and callback function
    var oldVal = window[name],
        newVal = oldVal,
        cbName = name + 'AsyncInit',
        timeout;
        
    
    // Creating 'watcher' object that will catch the real object
    Object.defineProperty(window, name, {

        configurable: true,
        enumerable: true,
        set: function(value) {
            
            // Assigning new value
            newVal = value;
    
            // Already fired callback
            if (typeof timeout === 'number') { return }

            // Property is undefined or empty
            // Some libraries assign empty object at first
            if (!Object.keys(newVal).length) { return }
            
            // Cleanup and fire callbacks next tick
            // Some libraries are not initialized fully until next tick
            timeout = setTimeout(function() {
    
                // Making us writable so we can be replaced
                Object.defineProperty(window, name, {writable: true});
    
                // Cleanup
                delete window[name];
    
                // Replacing 'watcher' with real object
                Object.defineProperty(window, name, {
                    configurable: true,
                    enumerable: true,
                    writable: true,
                    value: newVal
                });
                
                newVal = undefined;
                
                // Calling callback if exists
                if (typeof window[cbName] === 'function') {
                    // Pass in new value
                    window[cbName](window[name]);
                }
            }, 0);
        },
        get: function() {

            return newVal;
        }
    });
};