完美解决IE低版本不支持call与apply的问题

if(!Function.prototype.apply){
    Function.prototype.apply = function(obj, args){
        obj = obj == undefined ? window : Object(obj);//obj可以是js基本类型
        var i = 0, ary = [], str;
        if(args){
            for( len=args.length; i<len; i++ ){
                ary[i] = "args[" + i + "]";
            }
        }
        obj._apply = this;
        str = 'obj._apply(' + ary.join(',') + ')';
        try{
            return eval(str);
        }catch(e){
        }finally{
            delete obj._apply;
        }   
    };
}
if(!Function.prototype.call){
    Function.prototype.call = function(obj){
        var i = 1, args = [];
        for( len=arguments.length; i<len; i++ ){
            args[i-1] = arguments[i];
        }
        return this.apply(obj, args);
    };
}