10.添加script标签，判断onload是否完成

class Tools
{
static loadScript(url, callback)
{
let old_script = document.getElementById(url);
if (old_script)
{
if (old_script.ready == true)
{
// console.log("INFO:already load:" + url);
callback();
return;
}
else
{
document.body.removeChild(old_script);
// console.log("INFO:remove an old script that not ready:" + url);
}
}
let script = document.createElement('script');
script.id = url;
script.src = url;
script.onload = script.onreadystatechange = function() {
if (script.ready) {
return false;
}
if (!script.readyState //这是FF的判断语句，因为ff下没有readyState这个值，IE的readyState肯定有值
|| script.readyState == "loaded" || script.readyState == 'complete' // 这是IE的判断语句
) {
// console.log("INFO:load:" + url);
script.ready = true;
callback();
}
};
document.body.appendChild(script);
}
//synchronization
//同步加载多个脚本
static syncLoadScripts(scripts, callback)
{
var ok = 0;
var loadScript = function(url) {
Tools.loadScript(url, function(){
ok++;
// console.log("init:" + url)
if (ok == scripts.length) {
callback();
}
else {
loadScript(scripts[ok])
}
})
}
loadScript(scripts[0]);
}
//asynchronization
//异步加载多个脚本
static asyncLoadScripts(scripts, callback)
{
var ok = 0;
for (var i=0; i < scripts.length; i++) {
Tools.loadScript(scripts[i], function() {
console.log(scripts[ok])
ok++;
if (ok==scripts.length)
{
callback();
}
})
}
}
}
export default Tools;

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