实例详解js数组方法slice()的用法

var arr = [1, 2, 3, 'a', 'b', 'c', 'd'];
Array.prototype.copySlice =function() {
 var newArr = [];
 var len = this.length;
 var argLen = arguments.length;
 if(arguments.length == 1) {//一个参数
 var startNum = arguments[0] > 0 ? arguments[0] : (len + arguments[0]);
 for(var i = startNum; i < len; i++) {
 newArr.push(arr[i]);
 }
 }
 else if(arguments.length == 2) {//两个参数
 var startNum = arguments[0] > 0 ? arguments[0] : (len + arguments[0]);
 var endNum = arguments[1] > 0 ? arguments[1] : (len + arguments[1]);
 if(startNum >= endNum) {//起始索引大于终止索引，返回[]
 return newArr;
 }
 else {
 for(var i = startNum; i < endNum; i++) {
 newArr.push(arr[i]);
 }
 }
 }
 return newArr;
};
console.log(arr.length); // 7
// 一个参数
console.log(arr.copySlice(2)); // [3, "a", "b", "c", "d"]
// 两个参数
console.log(arr.copySlice(3, 6)); //["a", "b", "c"]
console.log(arr); //[1, 2, 3, "a", "b", "c", "d"]
// 接收负数
console.log(arr.copySlice(-2)); // ["c", "d"]
console.log(arr.copySlice(-5, 6)); //[3, "a", "b", "c"]
//结束位置小于起始位置，返回空数组。
console.log(arr.copySlice(-5, -6)); //[]
console.log(arr.copySlice(5, 5)); //[]
console.log(arr.copySlice(5, )); // ["c", "d"]