Question

2804. Array Prototype ForEach

中文文档

Description

Write your version of method forEach that enhances all arrays such that you can call the array.forEach(callback, context) method on any array and it will execute callback on each element of the array. Method forEach should not return anything.

callback accepts the following arguments:

• currentValue - represents the current element being processed in the array. It is the value of the element in the current iteration.
• index - represents the index of the current element being processed in the array.
• array - represents the array itself, allowing access to the entire array within the callback function.

The context is the object that should be passed as the function context parameter to the callback function, ensuring that the this keyword within the callback function refers to this context object.

Try to implement it without using the built-in array methods.

 

Example 1:

Input: 
arr = [1,2,3], 
callback = (val, i, arr) => arr[i] = val * 2, 
context = {"context":true}
Output: [2,4,6]
Explanation: 
arr.forEach(callback, context)  
console.log(arr) // [2,4,6]

The callback is executed on each element of the array.

Example 2:

Input: 
arr = [true, true, false, false], 
callback = (val, i, arr) => arr[i] = this, 
context = {"context": false}
Output: [{"context":false},{"context":false},{"context":false},{"context":false}]
Explanation: 
arr.forEach(callback, context) 
console.log(arr) // [{"context":false},{"context":false},{"context":false},{"context":false}]

The callback is executed on each element of the array with the right context.

Example 3:

Input: 
arr = [true, true, false, false], 
callback = (val, i, arr) => arr[i] = !val, 
context = {"context": 5}
Output: [false,false,true,true]

 

Constraints:

• arr is a valid JSON array
• context is a valid JSON object
• fn is a function
• 0 <= arr.length <= 105

Solutions

Solution 1

Array.prototype.forEach = function (callback: Function, context: any): void {
  for (let i = 0; i < this.length; ++i) {
    callback.call(context, this[i], i, this);
  }
};

/**
 *  const arr = [1,2,3];
 *  const callback = (val, i, arr) => arr[i] = val * 2;
 *  const context = {"context":true};
 *
 *  arr.forEach(callback, context)
 *
 *  console.log(arr) // [2,4,6]
 */