Accounting Format (Negative in Parentheses) Regex for JavaScript

What this pattern does

This page provides a comprehensive, battle-tested regular expression for matching accounting format (negative in parentheses), 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

// Accounting Format (Negative in Parentheses)
// ReDoS-safe | RegexVault — Finance > Currency & Money

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

function validateAccountingFormatNegativeInParentheses(input: string): boolean {
  return accountingFormatNegativeInParenthesesRegex.test(input);
}

// Example
console.log(validateAccountingFormatNegativeInParentheses("1,234.56")); // 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

Standard accounting/financial statement format. Parentheses denote debit or loss depending on context. Strip parentheses and negate when converting to numeric type for calculation.