TypeScript SIRET Validation Script (French company registration number)

validateRegistrationNumber.ts

// Returns true if valid, false if not. Note that registrationNumber param is a string (usually provided by HTML imput)
validateRegistrationNumber(registrationNumber: string): boolean {
  if (registrationNumber.length !== 14) {
    return false
  }
  let sum = 0
  let digit: number
  for (let i = 0; i < registrationNumber.length; i++) {
    if (i % 2 === 0) {
      digit = parseInt(registrationNumber.charAt(i), 10) * 2
      digit = digit > 9 ? (digit -= 9) : digit
    } else {
      digit = parseInt(registrationNumber.charAt(i), 10)
    }
    sum += digit
  }
  return sum % 10 === 0
}

A small TypeScript snippet to validate french company registration numbers, also called SIRET.

We are using Luhn Algorithm to validate the number. As the last SIRET Validation script I found was written in 2003 with the JavaScript of the time, I decided to refresh it a little.

Note that the function parameter is a string and not a number as it will probably come from an HTML input "text" (I found it more user-friendly than the input "number" for this kind of values). If you want to have an input "number", just replace registrationNumber
by registrationNumber.toString() within the function.