js异步加载Javascript代码示例详解

function getScript(url, success) {
    var script = document.createElement('script');
    script.src = url;
    var head = document.getElementsByTagName('head')[0],
    done = false;
   
    // Attach handlers for all browsers
    script.onload = script.onreadystatechange = function() {
        if (!done && (!this.readyState || this.readyState == 'loaded' || this.readyState == 'complete')) {
            done = true;
           
            // callback function provided as param
            success();
           
            script.onload = script.onreadystatechange = null;
            head.removeChild(script);
        };
    };
    head.appendChild(script);
};

if (typeof jQuery == 'undefined') {
    alert('Not found jQuery');
    getScript('http://ajax.googleapis.com/ajax/libs/jquery/1.4.4/jquery.min.js', function() {
        alert('jQuery loaded');
    });
}

//loadScript(url[,callback])
loadScript(“http://code.jquery.com/jquery.js”);
loadScript(“http://code.jquery.com/jquery.js”,function(){
console.log(1)
});
//loadScript(settings)
loadScript({“url”:”http://code.jquery.com/jquery.js”,”async”:false,”charset”:”utf-8〃,”cache”:false});
loadScript({“url”:”http://code.jquery.com/jquery.js”,”async”:false,”charset”:”utf-8〃,”success”:function(){
console.log(2)
}});
//或者你可以酱紫：
//loadScript(settings[,callback])
loadScript({“url”:”http://code.jquery.com/jquery.js”,”async”:false,”charset”:”utf-8〃},function(){
console.log($)
});

function loadScript(url,callback) {
var head = document.head || document.getElementsByTagName(“head”)[0] || document.documentElement,
script,
options,

if (typeof url === “object”) {
options = url;
url = undefined;
}
s = options || {};
url = url || s.url;
callback = callback || s.success;
script = document.createElement(“script”);
script.async = s.async || false;
script.type = “text/javascript”;
if (s.charset) {
script.charset = s.charset;
}
if(s.cache === false){
url = url+( /?/.test( url ) ? “&” : “?” )+ “_=” +(new Date()).getTime();
}
script.src = url;
head.insertBefore(script, head.firstChild);
if(callback){
document.addEventListener ? script.addEventListener(“load”, callback, false) : script.onreadystatechange = function() {
if (/loaded|complete/.test(script.readyState)) {
script.onreadystatechange = null
callback()
}
}
}
}