Pascal's triangle

index.js

import { pascal, binomePower } from "./math.js";

console.log(pascal(10)); // [1, 10, 45, 120, 210, 252, 210, 120, 45, 10, 1]
console.log(binomePower(3)); // "x^3 + 3x^2y + 3xy^2 + y^3"

math.js

export function pascal(l) {
  return l > 0 ? [0].concat(pascal(l - 1)).map((n, i, p) => n + (p[i + 1] || 0)) : [1];
}

export function binomePower(e) {
  return pascal(e).map(
    (c, i) => [
      c > 1 && c,
      e - i > 0 && "x",
      e - i > 1 && "^" + (e - i),
      i > 0 && "y",
      i > 1 && "^" + i,
    ].map(x => x || "").join("")
  ).join(" + ");
}