重寫forEach,map,filter,reduce等數組方法

直接上代碼

Array.prototype.myForEach = function (callback) {
    let arg2 = arguments[1] || window;
    for (let i = 0; i < this.length; i++) {
      callback.apply(arg2, [this[i], i, this]);
    }
  };

  Array.prototype.myMap = function (callback) {
    let arg2 = arguments[1] || window;
    let newArr = [];
    for (let i = 0; i < this.length; i++) {
      // 這裏須要對對象進行深拷貝，這裏就省略了
      newArr.push(callback.apply(arg2, [this[i], i, this]));
    }
    return newArr;
  };

  Array.prototype.myFilter = function (callback) {
    let arg2 = arguments[1] || window;
    let newArr = [];
    for (let i = 0; i < this.length; i++) {
       // 這裏須要對對象進行深拷貝，這裏就省略了
      callback.apply(arg2, [this[i], i, this]) ? newArr.push(this[i]) : newArr;
    }
    return newArr;
  };

  Array.prototype.myEvery = function (callback) {
    let arg2 = arguments[1] || window;
    let gate = true;
    for (let i = 0; i < this.length; i++) {
      if (!callback.apply(arg2, [this[i], i, this])) {
        gate = false;
        break;
      }
    }
    return gate;
  };

  Array.prototype.mySome = function (callback) {
    let arg2 = arguments[1] || window;
    let gate = false;
    for (let i = 0; i < this.length; i++) {
      if (callback.apply(arg2, [this[i], i, this])) {
        gate = true;
        break;
      }
    }
    return gate;
  };

  Array.prototype.myReduce = function (callback, initialValue) {
    for (let i = 0; i < this.length; i++) {
        // 這裏須要對對象進行深拷貝，這裏就省略了
      initialValue = callback(initialValue, this[i], i, this);
    }
    return initialValue;
  };

  Array.prototype.myReduceRight = function (callback, initialValue) {
    for (let i = this.length - 1; i >= 0; i--) {
        // 這裏須要對對象進行深拷貝，這裏就省略了
      initialValue = callback(initialValue, this[i], i, this);
    }
    return initialValue;
  };
複製代碼