web页面优化之动态加载js和文件

js无非就是script标签引入页面，但当项目越来越大的时候，单页面引入N个js显然不行，合并为单个文件减少了请求数，但请求的文件体积却很大。 这时候最好的做法就是按需引入，动态引入组件js和样式，文件load完成后调用callback，运行js。代码还是很简便的
1. 判断文件load完成。加载状态ie为onreadystatechange，其他为onload、onerror

if(isie){
Res.onreadystatechange = function(){
if(Res.readyState == 'complete' || Res.readyState == 'loaded'){
Res.onreadystatechange = null;
callback();
_self.loadedUi[modelName] = true;
}
}
}else{
Res.onload = function(){
Res.onload = null;
callback();
_self.loadedUi[modelName] = true;
}
Res.onerror = function(){
throw new Error('res error:' + modelName+'.js');
}
} 2. 所有组件的命名最好保持一致，callback调用也比较方便。还可以根据需要增加参数比如： requires，依赖于那些文件；style,true || false，是否加载样式，等等。
3. 移除操作也可以有，移除script、style标签、delete组件

(function(window,undefined){
if(!window.ui) {
window.ui = {};
}
//动态加载ui的js
window.bus = {
config : {
version : window.config.version,
cssPath : window.config.resServer + '/css/v3/ui',
jsPath : window.config.resServer + '/js/v2/ui'
},
loadedUi : {},
readyStateChange : function(){
var ua = navigator.userAgent.toLowerCase();
return ua.indexOf('msie') >= 0;
},
loadRes : function(modelName,prames,callback){
var _self = this;
var Res = document.createElement(prames.tagName);
for(var k in prames){
if(k != 'tagName'){
Res.setAttribute(k,prames[k],0);
}
}
document.getElementsByTagName('head')[0].appendChild(Res);
if(this.readyStateChange()){
Res.onreadystatechange = function(){
if(Res.readyState == 'complete' || Res.readyState == 'loaded'){
Res.onreadystatechange = null;
callback();
_self.loadedUi[modelName] = true;
}
}
}else{
Res.onload = function(){
Res.onload = null;
callback();
_self.loadedUi[modelName] = true;
}
Res.onerror = function(){
throw new Error('res error:' + modelName+'.js');
}
}
},
removeUi : function(modelName){
if(!modelName){
return true
};
this.loadedUi[modelName] = false;
var head = document.getElementsByTagName('head')[0];
var model_js = document.getElementById('J_model_'+modelName + '_js');
var model_css = document.getElementById('J_model_'+modelName + '_css');
if(model_js && model_css){
delete window.ui[modelName];
head.removeChild(model_js);
head.removeChild(model_css);
return true;
}else{
return false;
}
},
loadUi : function(modelName,callback,setting){
if(!modelName){
return true
};
callback = callback || function(){};
if(this.loadedUi[modelName] == true){
callback();
return true
}
var deafult_setting = {
style : true,
js : true,
requires : []
}
for(var key in setting){
deafult_setting[key] = setting[key];
}
deafult_setting['style'] === true && this.loadRes(modelName,{
id : 'J_model_'+modelName + '_css',
name : modelName,
tagName : 'link',
type : 'text/css',
rel : 'stylesheet',
href : this.config.cssPath + '/' + modelName + '.css?v=' + this.config.version
});
deafult_setting['js'] === true && this.loadRes(modelName,{
id : 'J_model_'+modelName + '_js',
name : modelName,
tagName : 'script',
type : 'text/javascript',
src : this.config.jsPath + '/' + modelName + '.js?v=' + this.config.version
},callback);
if(deafult_setting.requires.length > 0){
for(var i=0,len = deafult_setting.requires.length;i
this.loadUi(deafult_setting.requires[i]);
}
}
}
}
})(window)
使用方法
// load comment for feed
window.bus.loadUi('new_comment_feed', function(){
window.ui.new_comment_feed($("#J_newsList"));
},{
style : false,
requires:['emoticon','addFriend']
});
// load new yy ui
window.bus.loadUi('yy', function(){
window.ui.yy(options);
},{
style:false,
requires:['emoticon']
});
// load photoLightbox
window.bus.loadUi('photoLightbox', function(){
window.ui.photoLightbox(options.urlAjaxGetFriendPhoto, options.urlCommentOtherPhoto,$("#J_newsList"),options.myUid,options.myName);
}); 有用  |  无用 取消

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