Raw function as rule

Instead of using standard validators provided by bcx-validation, you can supply a raw function as validator.

const validateLength = value => {
  if (!(value && value.length >= 8)) {
    return 'must be at least 8 characters long';
  }
};

If value passed your validator, it should return nothing (null/undefined). Otherwise, return a string or array of strings as error message.

validation.validate('abc', validateLength);
// => ['must be at least 8 characters long']

This is not the only way a raw validator can return. It could return a shaped result like {isValid: false, message: "some error", break: true} for fine control of chain of validators. We will talk about it more in chain of rules.

A raw validator can also return a boolean. True means pass, false means fail with default error message “invalid”. validation.validate("abc", v => v && v.length >= 8); => ["invalid"].

Define new validator with function

Raw function validator is rarely used. It doesn’t take any of bcx-validation’s advantages. For re-usability, it’s better to add a new validator.

validation.addValidator('atLeast8Chars', value => {
  if (!(value && value.length >= 8)) {
    return 'must be at least 8 characters long';
  }
});

validation.validate('abc', {validate: 'atLeast8Chars'});
// or
validation.validate('abc', 'atLeast8Chars');
// => ['must be at least 8 characters long']

Now you can use value and error message override.

validation.validate('name#id_123#mark', {validate: 'atLeast8Chars',
                                         value: "_.split($value, '#')[1]",
                                         message: 'id must be at least 8 characters long'});
// => ['id must be at least 8 characters long']

You can wrap error message over existing error message.

validation.validate('name#id_123#mark', {validate: 'atLeast8Chars',
                                         value: "_.split($value, '#')[1]",
                                         message: 'id ${_.join($errors, ', ')}'});
// => ['id must be at least 8 characters long']

$errors is a special context variable only within error message override, it represents the original error messages array.

You might noticed the new validator we defined is quite bad for reuse. It could be better if the min length was passed in as option {validate: "atLeast", length: 8}. We will revisit this and show you how to support option in validator function after validator composition.

Let’s move on to chain of rules.