javascript利用apply和arguments复用方法
首先，有个单例对象，它上面挂了很多静态工具方法。其中有一个是each，用来遍历数组或对象。
varnativeForEach=[].forEach
varnativeMap=[].map
varutil={
each:function(obj,iterator,context){
if(obj==null)return
if(nativeForEach&&obj.forEach===nativeForEach){
obj.forEach(iterator,context)
}elseif(obj.length===+obj.length){
for(vari=0;i<obj.length;i++){
if(iterator.call(obj[i]||context,obj[i],i,obj)===true)return
}
}else{
for(varkinobj){
if(iterator.call(obj[k]||context,obj[k],k,obj)===true)return
}
}
},
map:function(obj,iterator,context){
varresults=[]
if(obj==null)returnresults
if(nativeMap&&obj.map===nativeMap)returnobj.map(iterator,context)
this.each(obj,function(val,i,coll){
results[i]=iterator.call(context,val,i,coll)
})
returnresults
}
}
还有诸如every、some等对集合(Array，Hash)操作的工具函数。使用时采用util.xx方式。
如果定义了一个集合类，这个类内部有集合数据。
functionCollection(data){
this.data=data||[]
//someotherproperty
//this.xxx=yyy
}
Collection.prototype={
//somemethod
}
可以很方便的把util上的方法拷贝到集合类上，如
这样拷贝后，Collection的实例就有了util上的方法，util操作的集合对象（第一个参数）就是Collection的this.data。如下直接可以遍历this.data了。
这种模式在很多开源库中使用，比如jQuery，它的$.each/$.map很方便的拷贝到了$().each/$().map。 又如Backbone，它的_.each/_.map/_.every/_.chain（还有很多）都拷贝到了Collection的原型上。
又有，把_.keys/_.values/_.pairs/_.invert/_.pick等对对象操作的实用方法拷贝了Backbone.Model上(1.0新增)
functioncopyMethod(clazz,obj){
for(varmethodinobj){
clazz.prototype[method]=function(){
varargs=[].slice.call(arguments)
vartarget=this.data
args.unshift(target)
obj[method].apply(obj,args)
}
}
}
copyMethod(Collection,util)
varcoll=newCollection([10,20,30])
//遍历
coll.each(function(k){
console.log(k)
})
//操作
vararr=coll.map(function(k){
returnk-5
})
console.log(arr)//5,15,25
//UnderscoremethodsthatwewanttoimplementontheCollection.
//90%ofthecoreusefulnessofBackboneCollectionsisactuallyimplemented
//righthere:
varmethods=["forEach","each","map","collect","reduce","foldl",
"inject","reduceRight","foldr","find","detect","filter","select",
"reject","every","all","some","any","include","contains","invoke",
"max","min","toArray","size","first","head","take","initial","rest",
"tail","drop","last","without","difference","indexOf","shuffle",
"lastIndexOf","isEmpty","chain"];
//MixineachUnderscoremethodasaproxyto`Collection#models`.
_.each(methods,function(method){
Collection.prototype[method]=function(){
varargs=slice.call(arguments);
args.unshift(this.models);
return_[method].apply(_,args);
};
});
varmodelMethods=["keys","values","pairs","invert","pick","omit"];
//MixineachUnderscoremethodasaproxyto`Model#attributes`.
_.each(modelMethods,function(method){
Model.prototype[method]=function(){
varargs=slice.call(arguments);
args.unshift(this.attributes);
return_[method].apply(_,args);
};
});
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