Array.prototype.fill

The fill() method changes all elements in an array to a static value, from a start index (default 0) to an end index (default array.length). It returns the modified array.

Syntax

fill(value)
fill(value, start)
fill(value, start, end)

Parameters

• value
  • : Value to fill the array with. Note all elements in the array will be this exact value: if value is an object, each slot in the array will reference that object.
• start optional
  • : Zero-based index at which to start filling, converted to an integer.
    • Negative index counts back from the end of the array — if start < 0, start + array.length is used.
    • If start < -array.length or start is omitted, 0 is used.
    • If start >= array.length, no index is filled.
• end optional
  • : Zero-based index at which to end filling, converted to an integer. fill() fills up to but not including end.
    • Negative index counts back from the end of the array — if end < 0, end + array.length is used.
    • If end < -array.length, 0 is used.
    • If end >= array.length or end is omitted, array.length is used, causing all indices until the end to be filled.
    • If end is positioned before or at start after normalization, no index is filled.

Return value

The modified array, filled with value.

Description

The fill() method is a mutating method. It does not alter the length of this, but it will change the content of this.

The fill() method fills empty slots in sparse arrays with value as well.

The fill() method is generic. It only expects the this value to have a length property. Although strings are also array-like, this method is not suitable to be applied on them, as strings are immutable.