abavalidator/src/aba-validation.ts

A validation module for browsers and Node.js to validate an American Bankers Association Routing Number used in ACH payments.

"use strict";
export function validate(routingNumber: string): boolean {
	const match = routingNumber.match(/^\s*([\d]{9})\s*$/);
	if (!match) {
		return false;
	}

	const weights = [3, 7 ,1];
	const aba = match[1];

	let sum = 0;
	for (let i=0 ; i<9 ; ++i) {
		sum += +aba.charAt(i) * weights[i % 3];
	}

	return (sum !== 0 && sum % 10 === 0);
}