Why is array.fill() not returning the modified array?

const array = ["apple"];
const paddedArray = array.fill("pear", 1, 3);
console.log(paddedArray.length);

Logs 1.

The Array.prototype.fill() type mentions:

Changes all array elements from start to end index to a static value and returns the modified array

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Why isn’t the modified array being returned?

>Solution :

Array#fill() does return the modified array. It is easy to check:

const array = ["apple"];
const paddedArray = array.fill("pear", 1, 3);
console.log(paddedArray.length);    // 1
console.log(array.length);          // 1
console.log(array === paddedArray); // literally the same object

What .fill() does not do is invent new indexes. It does not grow the array.

Only values be between the indexes 0 and length-1 are filled. From MDN, the description of the start and end parameters (respectively, second and third parameter) is:

start Optional

Zero-based index at which to start filling, converted to an integer.

[…]

• 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.

[…]

• If end >= array.length or end is omitted, array.length is used, causing all indices until the end to be filled.

[…]

Then the description reads:

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