Load a JavaScript file from the server, then execute it.

loadScript.js

/**
 * Load a JavaScript file from the server, then execute it.
 *
 * Code comes from `https://github.com/ded/script.js`
 * If your want more features, please follow the original
 * 
 * @usage: 
 *   loadScript('http://example.com/test.js', function() {
 *     console.log('Loaded')
 *   });
 */
function loadScript(jsFile, callback) {
    var el = document.createElement('script'), loaded
    el.onload = el.onerror = el.onreadystatechange = function() {
        if ((el.readyState && !(/^c|loade/.test(el.readyState))) || loaded) return;
        el.onload = el.onreadystatechange = null
        loaded = 1
        callback()
    }
    el.async = true
    el.src = jsFile;
    document.head.appendChild(el)
}