I need to find a way to fill an Array with a specific amount of nulls and only replace the last value with a specific number.
My idea would to create an empty Array, set Array.length = desiredLength and set Array[lastElement] = value. But how to fill the rest?
Example:
Input: Array should have a length of five and last value should be 123
Output: [null, null, null, null, 123]
You could fill the array with expected length minus 1 elements of null, spread that, and finally complemented with the last which is your expected element
Below demo should help you
const length = 5
const lastElem = 123
const res = [...Array(length - 1).fill(null), lastElem]
console.log(res)Try
array.fill(null, 0, array.length - 1)
And then
array[array.length - 1] = 123
fill part of Array or Array.prototype?
Array.prototypePerhaps
const arr = new Array(4).fill(null)
arr.push(123)
console.log(JSON.stringify(arr))Using Array.from()
const len = 5
const last = 123
const arr = Array.from({ length: len}, (_, i) => i < len - 1 ? null : last)
console.log(arr)You can also dynamically make a new array using Array.from or Array.apply, and either use the bult in map function for Array.from or call .map after Array.apply
ES6:
var filled=Array.from(
{length: 5},
(x,i, ar) => i < ar.length - 1 ? null : 123
)
ES5
var filled= Array.apply(0, {length: 5})
.map(function (x, i, ar) {
return i < ar.length -1 ? null : 123
})
use new Array() and Array.fill
function createNullFilledArray(arrayLength, lastValue) {
var arr = (new Array(arrayLength)).fill(null, 0, arrayLength - 1);
arr[arrayLength - 1] = lastValue;
return arr;
}
var outPut = createNullFilledArray(10, 123);
console.log(outPut);
Array(5).fill(null, 0, 4).fill(123, 4, 5)