Array.prototype.fill()

Baseline Widely available

This feature is well established and works across many devices and browser versions. Its been available across browsers since 2015 9.

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Array fill() . .

const array1 = [1, 2, 3, 4];

// Fill with 0 from position 2 until position 4
console.log(array1.fill(0, 2, 4));
// Expected output: Array [1, 2, 0, 0]

// Fill with 5 from position 1
console.log(array1.fill(5, 1));
// Expected output: Array [1, 5, 5, 5]

console.log(array1.fill(6));
// Expected output: Array [6, 6, 6, 6]

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

value

. . value , .

start Optional

0 , .

. start < 0 , start + array.length .
start < -array.length start , 0 .
start >= array.length, .

end Optional

0 , . fill() end , end .

. end < 0 , end + array.length .
end < -array.length , 0 .
end >= array.length end , array.length .
end , after , .

value .

fill() . this length , this .

fill() value .

fill() . this length . , .

: (length = 0) Array.prototype.fill() . Array.prototype.fill() 0 . .

fill()

console.log([1, 2, 3].fill(4)); // [4, 4, 4]
console.log([1, 2, 3].fill(4, 1)); // [1, 4, 4]
console.log([1, 2, 3].fill(4, 1, 2)); // [1, 4, 3]
console.log([1, 2, 3].fill(4, 1, 1)); // [1, 2, 3]
console.log([1, 2, 3].fill(4, 3, 3)); // [1, 2, 3]
console.log([1, 2, 3].fill(4, -3, -2)); // [4, 2, 3]
console.log([1, 2, 3].fill(4, NaN, NaN)); // [1, 2, 3]
console.log([1, 2, 3].fill(4, 3, 5)); // [1, 2, 3]
console.log(Array(3).fill(4)); // [4, 4, 4]

//      
const arr = Array(3).fill({}); // [{}, {}, {}]
arr[0].hi = "hi"; // [{ hi: "hi" }, { hi: "hi" }, { hi: "hi" }]

fill() 1

Octave MATLAB ones() 1 .

const arr = new Array(3);
for (let i = 0; i < arr.length; i++) {
  arr[i] = new Array(4).fill(1); //  4, 1   
}
arr[0][0] = 10;
console.log(arr[0][0]); // 10
console.log(arr[1][0]); // 1
console.log(arr[2][0]); // 1

fill()

. end .

const tempGirls = Array(5).fill("girl", 0);

. fill() .

fill()

fill() this length start end .

const arrayLike = { length: 2 };
console.log(Array.prototype.fill.call(arrayLike, 1));
// { '0': 1, '1': 1, length: 2 }

Specification
ECMAScript 2027 LanguageSpecification # sec-array.prototype.fill

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Array.prototype.fill()

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fill() 1

fill()

fill()

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