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，我已经开始将它用于几个不同的脚本

// 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');​

当遇到需要在加载后调用的脚本时出现问题：

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

所以我认为我会把它变成一个回调函数，可以这样使用：

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

我没想到这对我来说很难做到，但结果却是这样。

我的问题是在不过度复杂代码的情况下添加回调的最有效方法是什么。

  

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

Answer 1

感谢RASG

https://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

最新的片段：

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并未考虑IE9。以下是我找到的in the link proposed in the comments代码的修改版本。修改var baseUrl，以便它可以相应地找到脚本。

//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);
}

利用率：

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

Answer 3

其他答案很好用，但不是超级可读或需要Promises。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);
},