@howto/browser-modules/src/index.ts

A sample repo demonstrating package.json config for a browser module published to NPM

/**
 * Returns the sum of an unbounded array of integers
 */
export function sum(...numbers: any[]): number {
  const parsed = numbers.map((num) => parseInt(num, 10));

  if (parsed.some((num) => isNaN(num))) {
    throw new Error("Invalid numbers passed to `sum`");
  }

  return parsed.reduce((a, b) => a + b);
}

/**
 * Returns the difference of 2 integers
 */
export function difference(...numbers: any[]): number {
  if (numbers.length !== 2) {
    throw new Error("Incorrect number of parameters passed to `difference`");
  }
  let [start, end] = numbers;
  if (
    start === undefined ||
    start === null ||
    end === undefined ||
    end === null
  ) {
    throw new Error("`start` and `end` values not properly passed");
  }

  start = parseInt(start, 10);
  end = parseInt(end, 10);

  if (isNaN(start)) throw new Error("`start` is not a valid integer");
  if (isNaN(end)) throw new Error("`end` is not a valid integer");

  return Math.abs(end - start);
}