Array fill()

Truecodes 1 month ago 2 Comments

The fill() method serves to fill the array with the specified variables. it takes 3 parameters. They are value, start and end. Start and end values can be given on request. But it is imperative to enter value.

If start is negative, it is treated as length+start where length is the length of the array. If end is negative, it is treated as length+end.

fill () changes the structure of the array. ( it doesn’t just leave values like every )

 array.fill(value, start, end)

value :(Required) The value to fill the array.
start :(Optional) The index to start the array (default index is 0)
end :(Optional) The index to stop filling the array (default is array.length)

        var list = [1, 2, 3, 4, 5, 6];
        console.log(list.fill(9, 1, 3))
        console.log(list.fill(9, 3, 6))
        console.log(list.fill(9, 2))
        console.log(list.fill(9))

output:

[1, 9, 9, 4, 5, 6]
[1, 9, 9, 9, 9, 9]
[1, 9, 9, 9, 9, 9]
[9, 9, 9, 9, 9, 9]

Examples

Example 1 (negative value)

        let list1 = [2, 4, 6].fill(0, -3, -2)
        let list2 = [1,2,3].fill(0,-2,-1)
        console.log(list1)
        console.log(list2)

output:

[0, 4, 6]
[1, 0, 3]

Example 2 (worthless element)

        let list = [1, 2, 3].fill(2, NaN, NaN)
        console.log(list)

output:

[1, 2, 3]

Example 3

console.log(Array(5).fill("*"))

output:

[ * , * , * , * , * ]

Array fill() Polyfill

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

      if (this == null) {
        throw new TypeError('this is null or not defined');
      }

      var O = Object(this);

      var len = O.length >>> 0;

      var start = arguments[1];
      var relativeStart = start >> 0;

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

      var end = arguments[2];
      var relativeEnd = end === undefined ?
        len : end >> 0;

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

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

      return O;
    }
  });
}