Angular validator for 16 digit code which uniquely identifies an ORDCID id. See: https://learntech.imsu.ox.ac.uk/blog/angular-reactive-form-custom-validator-for-orcid/

orcid.validator.ts

import { AbstractControl, ValidationErrors, ValidatorFn } from '@angular/forms';

/*
 * Validator for 16 digit code which uniquely identifies an ORDCID id
 * Digit 16 is a chceksum for digits 1-15 - this validator checks that
 * Note: use other validators to check for valid Url which contains
 * https://orcid.org
 */
export function isORCIDValidator(control: AbstractControl): {[key: string]: any} | null {
    if (control.value) {  // don't check null values
        // split url up on /
        const urlParts: string[] = control.value.split('/');
        // get last digit
        const lastDigit = urlParts[urlParts.length - 1].slice(-1);
        // let's get numbers from last part (removing any hyphens, etc)
        const orcidDigits = urlParts[urlParts.length - 1].replace(/\D/g, '');
        // strip last digit
        const baseDigits = orcidDigits.slice(0, -1);
        // get check digit - 0-9 or X
        const generatedCheckDigit = generateCheckDigit(baseDigits).toString();
        if (generatedCheckDigit !== lastDigit) {
            return {'isORCID': {value: control.value}};  //return error
        }
    }
    return null;  //no errors
}

/**
  * Generates check digit as per ISO 7064 11,2.
  * https://support.orcid.org/knowledgebase/articles/116780-structure-of-the-orcid-identifier
  */
function generateCheckDigit(baseDigits: string) {
    let total = 0;
    for (let i = 0; i < baseDigits.length; i++) {
        const digit = parseInt(baseDigits.charAt(i), 10); // base 10
        total = (total + digit) * 2;
    }
    const remainder: number = total % 11;
    const result: number = (12 - remainder) % 11;
    return result === 10 ? 'X' : result;
}