It could be something like that:
var a = ['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j'];
var arrays = [], size = 3;
while (a.length > 0)
arrays.push(a.splice(0, size));
console.log(arrays);
See splice Array’s method.
An alternative method that does not mutate the array, beside create a shallow copy of it before chunk it, could be done by using slice and a for…loop:
var a = ['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j'];
var arrays = [], size = 3;
for (let i = 0; i < a.length; i += size)
arrays.push(a.slice(i, i + size));
console.log(arrays);
While a more functional programming oriented approach, could be:
const chunks = (a, size) =>
Array.from(
new Array(Math.ceil(a.length / size)),
(_, i) => a.slice(i * size, i * size + size)
);
let a = ['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j'];
console.log(chunks(a, 3));
console.log(chunks(a, 2));
See Array.from and how new Array(n) works, specifically.