validate-bi.js

export const validateBI = function (NBI, checkDigit) {
  return {
    valid: validateBI(NBI, checkDigit),
    errorMessage: 'BI não válido'
  }
}
  
const NBI_LENGTH = 9

function  calculateChecksum (number) {

    // Make the number into an array
    let numbers = [...number.toString()].map(Number)
    
    let sum = 0
    

    for (let i = 0; i < numbers.length - 1; i++) {
        sum += numbers[i] * (9 - i)
    }

    // check checksum
    return (sum % 11 && (11 - sum % 11) % 10) === numbers[numbers.length - 1]
}

function validateBI ( NBI , checkDigit ) {

    // Join NBI and the heck digit
    NBI = `${NBI}${checkDigit}`

    // Add zero to the left of NBI if it is of length 7   
    if ( NBI.length ===  8 ) {
        NBI = '0' + NBI
    }

    // If still not valid size, returh false
    if  (NBI.length != NBI_LENGTH) {
        return false
    }

    return  calculateChecksum(NBI)
}