Interface ReadonlyArray<T>

Readonly[unscopables]

Readonlylength

[iterator]

• "[iterator]"(): ArrayIterator<T>

• Iterator of values in the array.

  Returns ArrayIterator<T>

at

• at(index: number): T

• Returns the item located at the specified index.

  Parameters

  • index: number

    The zero-based index of the desired code unit. A negative index will count back from the last item.

  Returns T

concat

• concat(...items: ConcatArray<T>[]): T[]

• Combines two or more arrays.

  Parameters

  • ...items: ConcatArray<T>[]

    Additional items to add to the end of array1.

  Returns T[]
• concat(...items: (T | ConcatArray<T>)[]): T[]

• Combines two or more arrays.

  Parameters

  • ...items: (T | ConcatArray<T>)[]

    Additional items to add to the end of array1.

  Returns T[]

entries

• entries(): ArrayIterator<[number, T]>

• Returns an iterable of key, value pairs for every entry in the array

  Returns ArrayIterator<[number, T]>

every

• every<S>(
      predicate: (value: T, index: number, array: readonly T[]) => value is S,
      thisArg?: any,
  ): this is readonly S[]

• Determines whether all the members of an array satisfy the specified test.

  Type Parameters

  • S

  Parameters

  • predicate: (value: T, index: number, array: readonly T[]) => value is S

    A function that accepts up to three arguments. The every method calls the predicate function for each element in the array until the predicate returns a value which is coercible to the Boolean value false, or until the end of the array.
  • OptionalthisArg: any

    An object to which the this keyword can refer in the predicate function. If thisArg is omitted, undefined is used as the this value.

  Returns this is readonly S[]
• every(
      predicate: (value: T, index: number, array: readonly T[]) => unknown,
      thisArg?: any,
  ): boolean

• Determines whether all the members of an array satisfy the specified test.

  Parameters

  • predicate: (value: T, index: number, array: readonly T[]) => unknown

    A function that accepts up to three arguments. The every method calls the predicate function for each element in the array until the predicate returns a value which is coercible to the Boolean value false, or until the end of the array.
  • OptionalthisArg: any

    An object to which the this keyword can refer in the predicate function. If thisArg is omitted, undefined is used as the this value.

  Returns boolean

filter

• filter<S>(
      predicate: (value: T, index: number, array: readonly T[]) => value is S,
      thisArg?: any,
  ): S[]

• Returns the elements of an array that meet the condition specified in a callback function.

  Type Parameters

  • S

  Parameters

  • predicate: (value: T, index: number, array: readonly T[]) => value is S

    A function that accepts up to three arguments. The filter method calls the predicate function one time for each element in the array.
  • OptionalthisArg: any

    An object to which the this keyword can refer in the predicate function. If thisArg is omitted, undefined is used as the this value.

  Returns S[]
• filter(
      predicate: (value: T, index: number, array: readonly T[]) => unknown,
      thisArg?: any,
  ): T[]

• Returns the elements of an array that meet the condition specified in a callback function.

  Parameters

  • predicate: (value: T, index: number, array: readonly T[]) => unknown

    A function that accepts up to three arguments. The filter method calls the predicate function one time for each element in the array.
  • OptionalthisArg: any

    An object to which the this keyword can refer in the predicate function. If thisArg is omitted, undefined is used as the this value.

  Returns T[]

find

• find<S>(
      predicate: (value: T, index: number, obj: readonly T[]) => value is S,
      thisArg?: any,
  ): S

• Returns the value of the first element in the array where predicate is true, and undefined otherwise.

  Type Parameters

  • S

  Parameters

  • predicate: (value: T, index: number, obj: readonly T[]) => value is S

    find calls predicate once for each element of the array, in ascending order, until it finds one where predicate returns true. If such an element is found, find immediately returns that element value. Otherwise, find returns undefined.
  • OptionalthisArg: any

    If provided, it will be used as the this value for each invocation of predicate. If it is not provided, undefined is used instead.

  Returns S
• find(
      predicate: (value: T, index: number, obj: readonly T[]) => unknown,
      thisArg?: any,
  ): T

• Parameters

  • predicate: (value: T, index: number, obj: readonly T[]) => unknown
  • OptionalthisArg: any

  Returns T

findIndex

• findIndex(
      predicate: (value: T, index: number, obj: readonly T[]) => unknown,
      thisArg?: any,
  ): number

• Returns the index of the first element in the array where predicate is true, and -1 otherwise.

  Parameters

  • predicate: (value: T, index: number, obj: readonly T[]) => unknown

    find calls predicate once for each element of the array, in ascending order, until it finds one where predicate returns true. If such an element is found, findIndex immediately returns that element index. Otherwise, findIndex returns -1.
  • OptionalthisArg: any

    If provided, it will be used as the this value for each invocation of predicate. If it is not provided, undefined is used instead.

  Returns number

findLast

• findLast<S>(
      predicate: (value: T, index: number, array: readonly T[]) => value is S,
      thisArg?: any,
  ): S

• Returns the value of the last element in the array where predicate is true, and undefined otherwise.

  Type Parameters

  • S

  Parameters

  • predicate: (value: T, index: number, array: readonly T[]) => value is S

    findLast calls predicate once for each element of the array, in descending order, until it finds one where predicate returns true. If such an element is found, findLast immediately returns that element value. Otherwise, findLast returns undefined.
  • OptionalthisArg: any

    If provided, it will be used as the this value for each invocation of predicate. If it is not provided, undefined is used instead.

  Returns S
• findLast(
      predicate: (value: T, index: number, array: readonly T[]) => unknown,
      thisArg?: any,
  ): T

• Parameters

  • predicate: (value: T, index: number, array: readonly T[]) => unknown
  • OptionalthisArg: any

  Returns T

findLastIndex

• findLastIndex(
      predicate: (value: T, index: number, array: readonly T[]) => unknown,
      thisArg?: any,
  ): number

• Returns the index of the last element in the array where predicate is true, and -1 otherwise.

  Parameters

  • predicate: (value: T, index: number, array: readonly T[]) => unknown

    findLastIndex calls predicate once for each element of the array, in descending order, until it finds one where predicate returns true. If such an element is found, findLastIndex immediately returns that element index. Otherwise, findLastIndex returns -1.
  • OptionalthisArg: any

    If provided, it will be used as the this value for each invocation of predicate. If it is not provided, undefined is used instead.

  Returns number

flat

• flat<A, D extends number = 1>(this: A, depth?: D): FlatArray<A, D>[]

• Returns a new array with all sub-array elements concatenated into it recursively up to the specified depth.

  Type Parameters

  • A
  • D extends number = 1

  Parameters

  • this: A
  • Optionaldepth: D

    The maximum recursion depth

  Returns FlatArray<A, D>[]

flatMap

• flatMap<U, This = undefined>(
      callback: (
          this: This,
          value: T,
          index: number,
          array: T[],
      ) => U | ReadonlyArray<U>,
      thisArg?: This,
  ): U[]

• Calls a defined callback function on each element of an array. Then, flattens the result into a new array. This is identical to a map followed by flat with depth 1.

  Type Parameters

  • U
  • This = undefined

  Parameters

  • callback: (this: This, value: T, index: number, array: T[]) => U | ReadonlyArray<U>

    A function that accepts up to three arguments. The flatMap method calls the callback function one time for each element in the array.
  • OptionalthisArg: This

    An object to which the this keyword can refer in the callback function. If thisArg is omitted, undefined is used as the this value.

  Returns U[]

forEach

• forEach(
      callbackfn: (value: T, index: number, array: readonly T[]) => void,
      thisArg?: any,
  ): void

• Performs the specified action for each element in an array.

  Parameters

  • callbackfn: (value: T, index: number, array: readonly T[]) => void

    A function that accepts up to three arguments. forEach calls the callbackfn function one time for each element in the array.
  • OptionalthisArg: any

    An object to which the this keyword can refer in the callbackfn function. If thisArg is omitted, undefined is used as the this value.

  Returns void

includes

• includes(searchElement: T, fromIndex?: number): boolean

• Determines whether an array includes a certain element, returning true or false as appropriate.

  Parameters

  • searchElement: T

    The element to search for.
  • OptionalfromIndex: number

    The position in this array at which to begin searching for searchElement.

  Returns boolean

indexOf

• indexOf(searchElement: T, fromIndex?: number): number

• Returns the index of the first occurrence of a value in an array.

  Parameters

  • searchElement: T

    The value to locate in the array.
  • OptionalfromIndex: number

    The array index at which to begin the search. If fromIndex is omitted, the search starts at index 0.

  Returns number

join

• join(separator?: string): string

• Adds all the elements of an array separated by the specified separator string.

  Parameters

  • Optionalseparator: string

    A string used to separate one element of an array from the next in the resulting String. If omitted, the array elements are separated with a comma.

  Returns string

keys

• keys(): ArrayIterator<number>

• Returns an iterable of keys in the array

  Returns ArrayIterator<number>

lastIndexOf

• lastIndexOf(searchElement: T, fromIndex?: number): number

• Returns the index of the last occurrence of a specified value in an array.

  Parameters

  • searchElement: T

    The value to locate in the array.
  • OptionalfromIndex: number

    The array index at which to begin the search. If fromIndex is omitted, the search starts at the last index in the array.

  Returns number

map

• map<U>(
      callbackfn: (value: T, index: number, array: readonly T[]) => U,
      thisArg?: any,
  ): U[]

• Calls a defined callback function on each element of an array, and returns an array that contains the results.

  Type Parameters

  • U

  Parameters

  • callbackfn: (value: T, index: number, array: readonly T[]) => U

    A function that accepts up to three arguments. The map method calls the callbackfn function one time for each element in the array.
  • OptionalthisArg: any

    An object to which the this keyword can refer in the callbackfn function. If thisArg is omitted, undefined is used as the this value.

  Returns U[]

reduce

• reduce(
      callbackfn: (
          previousValue: T,
          currentValue: T,
          currentIndex: number,
          array: readonly T[],
      ) => T,
  ): T

• Calls the specified callback function for all the elements in an array. The return value of the callback function is the accumulated result, and is provided as an argument in the next call to the callback function.

  Parameters

  • callbackfn: (
        previousValue: T,
        currentValue: T,
        currentIndex: number,
        array: readonly T[],
    ) => T

    A function that accepts up to four arguments. The reduce method calls the callbackfn function one time for each element in the array.

  Returns T
• reduce(
      callbackfn: (
          previousValue: T,
          currentValue: T,
          currentIndex: number,
          array: readonly T[],
      ) => T,
      initialValue: T,
  ): T

• Parameters

  • callbackfn: (
        previousValue: T,
        currentValue: T,
        currentIndex: number,
        array: readonly T[],
    ) => T
  • initialValue: T

  Returns T

• reduce<U>(
      callbackfn: (
          previousValue: U,
          currentValue: T,
          currentIndex: number,
          array: readonly T[],
      ) => U,
      initialValue: U,
  ): U

• Calls the specified callback function for all the elements in an array. The return value of the callback function is the accumulated result, and is provided as an argument in the next call to the callback function.

  Type Parameters

  • U

  Parameters

  • callbackfn: (
        previousValue: U,
        currentValue: T,
        currentIndex: number,
        array: readonly T[],
    ) => U

    A function that accepts up to four arguments. The reduce method calls the callbackfn function one time for each element in the array.
  • initialValue: U

    If initialValue is specified, it is used as the initial value to start the accumulation. The first call to the callbackfn function provides this value as an argument instead of an array value.

  Returns U

reduceRight

• reduceRight(
      callbackfn: (
          previousValue: T,
          currentValue: T,
          currentIndex: number,
          array: readonly T[],
      ) => T,
  ): T

• Calls the specified callback function for all the elements in an array, in descending order. The return value of the callback function is the accumulated result, and is provided as an argument in the next call to the callback function.

  Parameters

  • callbackfn: (
        previousValue: T,
        currentValue: T,
        currentIndex: number,
        array: readonly T[],
    ) => T

    A function that accepts up to four arguments. The reduceRight method calls the callbackfn function one time for each element in the array.

  Returns T
• reduceRight(
      callbackfn: (
          previousValue: T,
          currentValue: T,
          currentIndex: number,
          array: readonly T[],
      ) => T,
      initialValue: T,
  ): T

• Parameters

  • callbackfn: (
        previousValue: T,
        currentValue: T,
        currentIndex: number,
        array: readonly T[],
    ) => T
  • initialValue: T

  Returns T

• reduceRight<U>(
      callbackfn: (
          previousValue: U,
          currentValue: T,
          currentIndex: number,
          array: readonly T[],
      ) => U,
      initialValue: U,
  ): U

• Calls the specified callback function for all the elements in an array, in descending order. The return value of the callback function is the accumulated result, and is provided as an argument in the next call to the callback function.

  Type Parameters

  • U

  Parameters

  • callbackfn: (
        previousValue: U,
        currentValue: T,
        currentIndex: number,
        array: readonly T[],
    ) => U

    A function that accepts up to four arguments. The reduceRight method calls the callbackfn function one time for each element in the array.
  • initialValue: U

    If initialValue is specified, it is used as the initial value to start the accumulation. The first call to the callbackfn function provides this value as an argument instead of an array value.

  Returns U

slice

• slice(start?: number, end?: number): T[]

• Returns a section of an array.

  Parameters

  • Optionalstart: number

    The beginning of the specified portion of the array.
  • Optionalend: number

    The end of the specified portion of the array. This is exclusive of the element at the index 'end'.

  Returns T[]

some

• some(
      predicate: (value: T, index: number, array: readonly T[]) => unknown,
      thisArg?: any,
  ): boolean

• Determines whether the specified callback function returns true for any element of an array.

  Parameters

  • predicate: (value: T, index: number, array: readonly T[]) => unknown

    A function that accepts up to three arguments. The some method calls the predicate function for each element in the array until the predicate returns a value which is coercible to the Boolean value true, or until the end of the array.
  • OptionalthisArg: any

    An object to which the this keyword can refer in the predicate function. If thisArg is omitted, undefined is used as the this value.

  Returns boolean

toLocaleString

• toLocaleString(): string

• Returns a string representation of an array. The elements are converted to string using their toLocaleString methods.

  Returns string
• toLocaleString(
      locales: string | string[],
      options?: NumberFormatOptions & DateTimeFormatOptions,
  ): string

• Parameters

  • locales: string | string[]
  • Optionaloptions: NumberFormatOptions & DateTimeFormatOptions

  Returns string

toReversed

• toReversed(): T[]

• Copies the array and returns the copied array with all of its elements reversed.

  Returns T[]

toSorted

• toSorted(compareFn?: (a: T, b: T) => number): T[]

• Copies and sorts the array.

  Parameters

  • OptionalcompareFn: (a: T, b: T) => number

    Function used to determine the order of the elements. It is expected to return a negative value if the first argument is less than the second argument, zero if they're equal, and a positive value otherwise. If omitted, the elements are sorted in ascending, ASCII character order.

    [11, 2, 22, 1].toSorted((a, b) => a - b) // [1, 2, 11, 22]
    Copy

  Returns T[]

toSpliced

• toSpliced(start: number, deleteCount: number, ...items: T[]): T[]

• Copies an array and removes elements while, if necessary, inserting new elements in their place, returning the remaining elements.

  Parameters

  • start: number

    The zero-based location in the array from which to start removing elements.
  • deleteCount: number

    The number of elements to remove.
  • ...items: T[]

    Elements to insert into the copied array in place of the deleted elements.

  Returns T[]

  A copy of the original array with the remaining elements.
• toSpliced(start: number, deleteCount?: number): T[]

• Copies an array and removes elements while returning the remaining elements.

  Parameters

  • start: number

    The zero-based location in the array from which to start removing elements.
  • OptionaldeleteCount: number

    The number of elements to remove.

  Returns T[]

  A copy of the original array with the remaining elements.

toString

• toString(): string

• Returns a string representation of an array.

  Returns string

values

• values(): ArrayIterator<T>

• Returns an iterable of values in the array

  Returns ArrayIterator<T>

with

• with(index: number, value: T): T[]

• Copies an array, then overwrites the value at the provided index with the given value. If the index is negative, then it replaces from the end of the array

  Parameters

  • index: number

    The index of the value to overwrite. If the index is negative, then it replaces from the end of the array.
  • value: T

    The value to insert into the copied array.

  Returns T[]

  A copy of the original array with the inserted value.