javascript split array into chunks

function splitArrayIntoChunksOfLen(arr, len) {
  var chunks = [], i = 0, n = arr.length;
  while (i < n) {
    chunks.push(arr.slice(i, i += len));
  }
  return chunks;
}
var alphabet=['a','b','c','d','e','f'];
var alphabetPairs=splitArrayIntoChunksOfLen(alphabet,2); //split into chunks of two

let input = [1,2,3,4,5,6,7,8,9];
let chunked = []
let size = 2;

for (let i = 0;  i < input.length; i += size) {
  chunked.push(input.slice(i, i + size))
}
console.log(chunked)

Array.prototype.chunk = function(size) {
    let result = [];
    
    while(this.length) {
        result.push(this.splice(0, size));
    }
        
    return result;
}

const arr = [1, 2, 3, 4, 5, 6, 7, 8, 9];
console.log(arr.chunk(2));