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"]