Thungghuan / js-functions-rewriting

Trying to rewrite some basic functions and methods in JavaScript.

js-functions-rewriting

This project is trying to rewrite the basic JavaScript functions and methods, such as the methods in Array.prototype, which will help JavaScript learners (including myself) to use these functions and methods better.

Function list

Here comes the functions that this project will rewrite.

Array methods

• Array.prototype.concat()

• Array.prototype.filter()

• Array.prototype.find()

• Array.prototype.findIndex()

• Array.prototype.flat()

• Array.prototype.indexOf()

• Array.prototype.join()

• Array.prototype.lastIndexOf()

• Array.prototype.map()

• Array.prototype.pop()

  The pop() method removes the last element from an array and returns that element. This method changes the length of the array.

  Return value

  The removed element from the array; undefined if the array is empty

  const plants = ['broccoli', 'cauliflower', 'cabbage', 'kale', 'tomato']
  var popped = plants.pop()
  
  console.log(plants)  // ['broccoli', 'cauliflower', 'cabbage', 'kale']
  console.log(popped)  // 'tomato'

• Array.prototype.push()

  The push() method adds one or more elements to the end of an array and returns the new length of the arrays.

  Parameters elements

  The element(s) to add to the end of the array.

  Return value

  The new length property of the object upon which the method was called.

  const animals = ['pigs', 'goats', 'sheep']
  const count = animals.push('cows', 'dogs')
  
  console.log(animals)  // ['pigs', 'goats', 'sheep', 'cows', 'dogs']
  console.log(count)  // 5

• Array.prototype.reduce()

• Array.prototype.reduceRight()

• Array.prototype.reverse()

  The reverse() method reverses an array in place. The first array element becomes the last, and the last array element becomes the first.

  Return value

  The reversed array.

  const a = [1, 2, 3];
  console.log(a);  // [1, 2, 3]
  
  b = a.reverse();
  console.log(a);  // [3, 2, 1]
  console.log(b);  // [3, 2, 1]

• Array.prototype.shift()

  The shift() method removes the first element from an array and returns that removed element. This method changes the length of the array.

  Return value

  The removed element from the array; undefined if the array is empty.

  const array = [1, 2, 3]
  const firstElement = array.shift()
  
  console.log(array)  // [2, 3]
  console.log(firstElement)  // 1

• Array.prototype.slice()

  The slice() method returns a shallow copy of a portion of a n array into a new array object selected from start to end (end not included) where start and end represent the index of items in that array. The original array will not be modified.

  Parameters start (Optional)

  Zero-based index at which to start extraction.

  A negative index can be used, indicating an offset from th end of the sequence. slice(-2) extracts the last two elements in the sequence.

  If start is undefined, slice starts from the index 0.

  If start is greater than the index range of the sequence, an empty array is returned.

  end (Optional)

  Zero-based index before which to end extraction. slice extracts up to but not including end. For example, slice(1, 4) extracts the second element through the fourth element (elements indexed 1, 2, and 3).

  A negative index can be used, indicating an offset from the end of the sequence. slice(2, -1) extracts the third element through the second-to-last element in the sequence.

  If end is omitted, slice extracts through the end of the sequence (arr.length).

  If end is greater than the length of the sequence, slice extracts through to end of the sequence (arr.length).

  Return value

  A new array containing the extracted elements.

• Array.prototype.some()

• Array.prototype.sort()

• Array.prototype.splice()

• Array.prototype.unshift()

  The unshift() method adds one or more elements to the beginning of an array and returns the new length of the array.

  Parameters elements

  The element(s) to add to the front of the arr

  Return value

  The new length property of the object upon which the method was called.

  let arr = [4, 5, 6]
  let length = arr.unshift(1, 2, 3)
  
  console.log(arr)  // [1, 2, 3, 4, 5, 6]
  console.log(length)  // 6
  
  arr.unshift(1)
  arr.unshift(2)
  arr.unshift(3)
  
  console.log(arr)  // [3, 2, 1, 1, 2, 3, 4, 5, 6]
  console.log(length)  // 9

String methods

• String.prototype.replace()
• String.prototype.replaceAll()
• String.prototype.slice()
• String.prototype.split()
• String.prototype.strike()
• String.prototype.substr()
• String.prototype.substring()