Large Number with Thousands Separator Regex for JavaScript

What this pattern does

This page provides a well-structured, multi-part regular expression for matching large number with thousands separator, ported and verified for JavaScript. Financial data validation has zero tolerance for false negatives — a missed invalid entry can corrupt downstream calculations. The snippet below is ready to drop into your JavaScript project — whether you're validating in an Express middleware, a Next.js API route, or a client-side form.

Javascript Implementation

// Large Number with Thousands Separator
// ReDoS-safe | RegexVault — Finance > Currency & Money

const largeNumberWithThousandsSeparatorRegex = /^(?:[1-9][0-9]{0,2}(?:,[0-9]{3})*|0)$/;

function validateLargeNumberWithThousandsSeparator(input: string): boolean {
  return largeNumberWithThousandsSeparatorRegex.test(input);
}

// Example
console.log(validateLargeNumberWithThousandsSeparator("0")); // true

Test Cases

When to use this pattern

This pattern is drawn from the Finance > Currency & Money category and carries a ReDoS-safe certification. That matters for JavaScript developers because especially critical in long-running Node.js event loops where a ReDoS vulnerability can block the entire process. RegexVault audits patterns against known backtracking attack vectors, ensuring you have the necessary context before using this regex in a high-stakes production environment.

Common Pitfalls

Technical Notes

Enforces proper comma grouping — 1000 is rejected (missing comma), 1,00 is rejected (wrong grouping). For European dot-separated format (1.000.000), swap comma/dot in the pattern.