prefill-an-array.md

Prefill an Array ^{6 Kyu}

^{LINK TO THE KATA - ARRAYS FUNDAMENTALS}

Description

Create the function prefill that returns an array of n elements that all have the same value v. See if you can do this without using a loop.

You have to validate input:

• v can be anything (primitive or otherwise)
• if v is ommited, fill the array with undefined
• if n is 0, return an empty array
• if n is anything other than an integer or integer-formatted string (e.g. '123') that is >=0, throw a TypeError

When throwing a TypeError, the message should be n is invalid, where you replace n for the actual value passed to the function.

Code Examples

prefill(3,1) --> [1,1,1]

prefill(2,"abc") --> ['abc','abc']

prefill("1", 1) --> [1]

prefill(3, prefill(2,'2d')) --> [['2d','2d'],['2d','2d'],['2d','2d']]

prefill("xyz", 1) --> throws TypeError with message "xyz is invalid"

Solution

const prefill = (n, v) => {
  if (!Number.isInteger(+n) || n < 0 || n != parseInt(n)) {
    throw new TypeError(n + ' is invalid')
  }

  return new Array(Number(n)).fill(v)
}