实现JavaScript forEach

    function forEach(list, callback){
        for(var n = 0; n <list.length; n++){
            callback.call(list[n], n);
        }
    }
    var arr = [1,2,3,4,5,6,7,8]
    forEach(arr, function(index){
        if(this == arr[index]){
            console.log("Got the expected value of " + arr[index]);
        }
    })