5kyu_PrefillAnArray.js

// 5kyu - Prefill an Array

// 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"


function prefill(n, v){
    if (parseInt(n) !== Math.abs(n)) { throw new TypeError(`${n} is invalid`); }
    return Array.apply(null, Array(+n)).map(function (d,i) { return v });
}