JS: Array.prototype.fill

(new in ECMAScript 2015)

xArray.fill(value)

• Modify the array by giving a value to all indexes, including missing indexes in Sparse Array.
• Return the modified xArray.

// using fill on array constructor result
console.log(
 Array(4).fill(0),
);
// [ 0, 0, 0, 0 ]

// using fill to change all values of a array
const xx = [0, 1, 2];
console.log(xx.fill(7));
// [ 7, 7, 7 ]
console.log(xx);
// [ 7, 7, 7 ]

// using fill to fill sparse array
const xx = [];
xx.length = 4;
xx.fill(0);
console.log(xx);
// [ 0, 0, 0, 0 ]

xArray.fill(value, startIndex)

Fill start from startIndex

console.log(
 [0, 1, 2, 3].fill("x", 0),
);
// [ "x", "x", "x", "x" ]

console.log(
 [0, 1, 2, 3].fill("x", 1),
);
// [ 0, "x", "x", "x" ]

console.log(
 [0, 1, 2, 3].fill("x", 2),
);
// [ 0, 1, "x", "x" ]

console.log(
 [0, 1, 2, 3].fill("x", 3),
);
// [ 0, 1, 2, "x" ]

console.log(
 [0, 1, 2, 3].fill("x", 4),
);
// [ 0, 1, 2, 3 ]

xArray.fill(value, startIndex, endIndex)

Replace up to endIndex, not including it.

console.log(
 [0, 1, 2, 3].fill("x", 0, 0),
);
// [ 0, 1, 2, 3 ]

console.log(
 [0, 1, 2, 3].fill("x", 0, 1),
);
// [ "x", 1, 2, 3 ]

console.log(
 [0, 1, 2, 3].fill("x", 0, 2),
);
// [ "x", "x", 2, 3 ]

console.log(
 [0, 1, 2, 3].fill("x", 0, 3),
);
// [ "x", "x", "x", 3 ]

console.log(
 [0, 1, 2, 3].fill("x", 0, 4),
);
// [ "x", "x", "x", "x" ]