Array.prototype.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]

arr.fill(value[, start = 0[, end = this.length]])

value

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end

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[start, end).

fill value, start end. start end , 0 length this .

start , length+start, length . end , length+end.

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[1, 2, 3].fill(4);               // [4, 4, 4]
[1, 2, 3].fill(4, 1);            // [1, 4, 4]
[1, 2, 3].fill(4, 1, 2);         // [1, 4, 3]
[1, 2, 3].fill(4, 1, 1);         // [1, 2, 3]
[1, 2, 3].fill(4, 3, 3);         // [1, 2, 3]
[1, 2, 3].fill(4, -3, -2);       // [4, 2, 3]
[1, 2, 3].fill(4, NaN, NaN);     // [1, 2, 3]
[1, 2, 3].fill(4, 3, 5);         // [1, 2, 3]
Array(3).fill(4);                // [4, 4, 4]
[].fill.call({ length: 3 }, 4);  // {0: 4, 1: 4, 2: 4, length: 3}

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

if (!Array.prototype.fill) {
  Object.defineProperty(Array.prototype, 'fill', {
    value: function(value) {

      //  1-2.
      if (this == null) {
        throw new TypeError('this is null or not defined');
      }

      var O = Object(this);

      //  3-5.
      var len = O.length >>> 0;

      //  6-7.
      var start = arguments[1];
      var relativeStart = start >> 0;

      //  8.
      var k = relativeStart < 0 ?
        Math.max(len + relativeStart, 0) :
        Math.min(relativeStart, len);

      //  9-10.
      var end = arguments[2];
      var relativeEnd = end === undefined ?
        len : end >> 0;

      //  11.
      var final = relativeEnd < 0 ?
        Math.max(len + relativeEnd, 0) :
        Math.min(relativeEnd, len);

      //  12.
      while (k < final) {
        O[k] = value;
        k++;
      }

      //  13.
      return O;
    }
  });
}

JavaScript, Object.defineProperty, Array.prototype, .

• Array
• TypedArray.prototype.fill()