异步脚本加载回调

Question

http://jsfiddle.net/JamesKyle/HQDu6/

我创建了一个基于Mathias Bynens Optimization of the Google Analytics asynchronous script 的简短函数，如下所示：

function async(src) {
  var d = document, t = 'script',
      o = d.createElement(t),
      s = d.getElementsByTagName(t)[0];
  o.src = '//' + src;
  s.parentNode.insertBefore(o, s);
}

这很好用，我已经开始在几个不同的脚本中使用它

// Crazy Egg
async('dnn506yrbagrg.cloudfront.net/pages/scripts/XXXXX/XXXXX.js?' + Math.floor(new Date().getTime() / 3600000));

// User Voice
var uvOptions = {};
async('widget.uservoice.com/XXXXX.js');

// Google Analytics
var _gaq = [['_setAccount', 'UA-XXXXX-XX'], ['_setDomainName', 'coachup.com'], ['_trackPageview']];
async('google-analytics.com/ga.js');

// Stripe
async('js.stripe.com/v1');​

当我遇到一个脚本加载后需要调用时，问题就来了：

// Snap Engage
async('snapabug.appspot.com/snapabug.js');
SnapABug.init('XXXXX-XXXXX-XXXXX-XXXXX-XXXXX');

所以我想我会把它变成一个回调函数，这样可以使用：

async('snapabug.appspot.com/snapabug.js', function() {
    SnapABug.init('XXXXX-XXXXX-XXXXX-XXXXX-XXXXX');
});

我没想到这对我来说会很困难，但事实证明就是这样。

我的问题是在不使代码过于复杂的情况下添加回调的最有效方法是什么。

查看 jsfiddle：http://jsfiddle.net/JamesKyle/HQDu6/

Answer 1

感谢RASGhttps://stackoverflow.com/a/3211647/982924

带回调的异步函数：

function async(u, c) {
  var d = document, t = 'script',
      o = d.createElement(t),
      s = d.getElementsByTagName(t)[0];
  o.src = '//' + u;
  if (c) { o.addEventListener('load', function (e) { c(null, e); }, false); }
  s.parentNode.insertBefore(o, s);
}

用法：

async('snapabug.appspot.com/snapabug.js', function() {
    SnapABug.init('XXXXX-XXXXX-XXXXX-XXXXX-XXXXX');
});

jsFiddle

Answer 2

一个更新的sn-p：

async function loadAsync(src) {
    const script = document.createElement('script');
    script.src = src;
    return new Promise((resolve, reject) => {
        script.onreadystatechange = function () {
            if (script.readyState === 'loaded' || script.readyState === 'complete') {
                script.onreadystatechange = null;
                resolve(true);
            }
        };
        document.getElementsByTagName('head')[0].appendChild(script);
    });
}

利用

  loadAsync(`https://....js`).then(_ => {
    //  ... script loaded here
  })

---

James Kyle's answer 不考虑 IE9。这是我找到的代码的修改版本in the link proposed in the comments。修改 var baseUrl 以便它可以找到相应的脚本。

//for requiring a script loaded asynchronously.
function loadAsync(src, callback, relative){
    var baseUrl = "/resources/script/";
    var script = document.createElement('script');
    if(relative === true){
        script.src = baseUrl + src;  
    }else{
        script.src = src; 
    }

    if(callback !== null){
        if (script.readyState) { // IE, incl. IE9
            script.onreadystatechange = function() {
                if (script.readyState === "loaded" || script.readyState === "complete") {
                    script.onreadystatechange = null;
                    callback();
                }
            };
        } else {
            script.onload = function() { // Other browsers
                callback();
            };
        }
    }
    document.getElementsByTagName('head')[0].appendChild(script);
}

利用：

loadAsync('https://www.gstatic.com/charts/loader.js' , function(){
    chart.loadCharts();
    });
// OR relative path
loadAsync('fastclick.js', null, true);

Answer 3

其他答案效果很好，但不是超级可读或需要承诺。这是我的两分钱：

function loadScript(src, callback) {
    var script = document.createElement('script');
    script.setAttribute('src', src);
    script.addEventListener('load', callback);
    document.head.appendChild(script);
},