Array<T>.prototype.*

• concat(...items: (T | Array<T>)[]): T[] 🔒 ^ES3

  Returns a new array that is the concatenation of this and all items. Non-array parameters are treated as if they were arrays with single elements.

  > ['a'].concat('b', ['c', 'd'])
  [ 'a', 'b', 'c', 'd' ]
  

• copyWithin(target: number, start: number, end=this.length): this ✏️ ^ES6

  Copies the elements whose indices range from start to (excl.) end to indices starting with target. Overlapping is handled correctly.

  > ['a', 'b', 'c', 'd'].copyWithin(0, 2, 4)
  [ 'c', 'd', 'c', 'd' ]
  

• entries(): Iterable<[number, T]> 🔒 ^ES6

  Returns an iterable over [index, element] pairs.

  > Array.from(['a', 'b'].entries())
  [ [ 0, 'a' ], [ 1, 'b' ] ]
  

• every(callback: (value: T, index: number, array: Array<T>) => boolean, thisArg?: any): boolean 🔒 ^ES5

  Returns true if callback returns true for every element. Stops as soon as it receives false. Math: ∀

  > [1, 2, 3].every(x => x > 0)
  true
  > [1, -2, 3].every(x => x > 0)
  false
  

• fill(value: T, start=0, end=this.length): this ✏️ ^ES6

  • Assigns value to every index.
  • [0, 1, 2].fill('a') → [ 'a', 'a', 'a' ]

• filter(callback: (value: T, index: number, array: Array<T>) => any, thisArg?: any): T[] 🔒 ^ES5

  • Returns an array with only those elements for which callback returns true.
  • [1, -2, 3].filter(x => x > 0) → [ 1, 3 ]

• find(predicate: (value: T, index: number, obj: T[]) => boolean, thisArg?: any): T | undefined 🔒 ^ES6

  • The result is the first element for which predicate returns true. If it never does, the result is undefined.
  • [1, -2, 3].find(x => x < 0) → -2
  • [1, 2, 3].find(x => x < 0) → undefined

• findIndex(predicate: (value: T, index: number, obj: T[]) => boolean, thisArg?: any): number 🔒 ^ES6

  • The result is the index of the first element for which predicate returns true. If it never does, the result is -1.
  • [1, -2, 3].findIndex(x => x < 0) → 1
  • [1, 2, 3].findIndex(x => x < 0) → -1

• forEach(callback: (value: T, index: number, array: Array<T>) => void, thisArg?: any): void 🔒 ^ES5

  • Calls callback for each element.
  • ['a', 'b'].forEach((x, i) => console.log(x, i))

• includes(searchElement: T, fromIndex=0): boolean 🔒 ^ES2016

  • Returns true if searchElement is an element and false, otherwise.
  • [0, 1, 2].includes(1) → true
  • [0, 1, 2].includes(5) → false

• indexOf(searchElement: T, fromIndex=0): number 🔒 ^ES5

  • Returns the index of the first element that is strictly equal to searchElement. Returns -1 if there is no such element. Starts searching at index fromIndex, visiting subsequent indices next.
  • ['a', 'b', 'a'].indexOf('a') → 0
  • ['a', 'b', 'a'].indexOf('a', 1) → 2
  • ['a', 'b', 'a'].indexOf('c') → -1

• join(separator = ','): string 🔒 ^ES1

  • Creates a string by concatenating string representations of all elements, separating by separator.
  • ['a', 'b', 'c'].join() → 'a,b,c'
  • ['a', 'b', 'c'].join('##') → 'a##b##c'

• keys(): Iterable<number> 🔒 ^ES6

  • Returns an iterable over the keys of the array.
  • [...['a', 'b'].keys()] → [ 0, 1 ]

• lastIndexOf(searchElement: T, fromIndex=this.length-1): number 🔒 ^ES5

  • Returns the index of the first element that is strictly equal to searchElement. Returns -1 if there is no such element. Starts searching at index fromIndex, visiting preceding indices next.
  • ['a', 'b', 'a'].lastIndexOf('a') → 2
  • ['a', 'b', 'a'].lastIndexOf('a', 1) → 0
  • ['a', 'b', 'a'].lastIndexOf('c') → -1

• map<U>(callback: (value: T, index: number, array: ReadonlyArray<T>) => U, thisArg?: any): U[] 🔒 ^ES5

  • Returns a new array, in which every element is the result of callback being applied to the corresponding element of this.
  • [1, 2, 3].map(x => x * 2) → [ 2, 4, 6 ]
  • ['a', 'b', 'c'].map((x, i) => i) → [ 0, 1, 2 ]

• pop(): T | undefined ✏️ ^ES3

  Treats the end of the array as a stack and removes the last element.

  > const arr = ['a', 'b', 'c'];
  undefined
  > arr.pop()
  'c'
  > arr
  [ 'a', 'b' ]
  

• push

• reduce

• reduceRight

• reverse

• shift

• slice

• some

• sort

• splice

• toLocaleString

• toString

• unshift

• values(): Iterable<T>

How holes are handled is described in Sect. “Array operations and holes” in “Exploring ES6”.