ABN Validation

/**
 * @description Validate ABN numbers
 *
 * @param {string} abn
 * @return {boolean} is ABN number valid
 *
 * 0. ABN must be 11 digits long
 * 1. Subtract 1 from the first (left) digit to give a new eleven digit number
 * 2. Multiply each of the digits in this new number by its weighting factor
 * 3. Sum the resulting 11 products
 * 4. Divide the total by 89, noting the remainder
 * 5. If the remainder is zero the number is valid
 */
export function validateABN(abn) {
  let isValid = true
 
  // remove all spaces
  abn = abn.replace(/\s/g, '')
 
  // 0. ABN must be 11 digits long
  isValid = abn && /^\d{11}$/.test(abn)
 
  if (isValid) {
    let weightedSum = 0
    let weight = [10, 1, 3, 5, 7, 9, 11, 13, 15, 17, 19]
 
    // Rules: 1,2,3
    let i
    for (i = 0; i < weight.length; i++) {
      weightedSum += (parseInt(abn[i], 16) - (i === 0 ? 1 : 0)) * weight[i]
    }
 
    // Rules: 4,5
    isValid = isValid && weightedSum % 89 === 0
  }
 
  return isValid
}

validateABN("51824753556") // true
validateABN("51 824 753 556") // true
validateABN("51824744556") // false