Function patternValidator

packages/forms/src/validators.ts:569–596

(pattern: string | RegExp)

 * See `Validators.pattern` for additional information.
 */
export function patternValidator(pattern: string | RegExp): ValidatorFn {
  if (!pattern) return nullValidator;
  let regex: RegExp;
  let regexStr: string;
  if (typeof pattern === 'string') {
    regexStr = '';

    if (pattern.charAt(0) !== '^') regexStr += '^';

    regexStr += pattern;

    if (pattern.charAt(pattern.length - 1) !== '$') regexStr += '$';

    regex = new RegExp(regexStr);
  } else {
    regexStr = pattern.toString();
    regex = pattern;
  }
  return (control: AbstractControl): ValidationErrors | null => {
    if (isEmptyInputValue(control.value)) {
      return null; // don't validate empty values to allow optional controls
    }
    const value: string = control.value;
    return regex.test(value)
      ? null
      : {'pattern': {'requiredPattern': regexStr, 'actualValue': value}};
  };
}

/**
 * Function that has `ValidatorFn` shape, but performs no operation.