yup-universal-locale

Build perfectly integrated extensions to yup by registering custom validation method messages to the locale.

Improved localisation

Yup offers a setLocale method, allowing users to set custom default messages for validations. Unfortunately this only works for the built-in validations that Yup ships with - custom tests cannot access this locale, which means that if you supply new validations, users have no means of customising or translating the default message for them.

yup-universal-locale plugs this gap. Users of your validations don't have to do anything special or import anything - it's sufficient for you to import yup-universal-locale before defining your validations.

import { string, addMethod } from 'yup';
import 'yup-universal-locale';

// create a custom validation
addMethod(string, 'mustNotContain', function(stringToExclude, message) {
  return this.test({
    // the `name` is crucial: it determines the lookup in the locale
    name: 'mustNotContain', 
    message: message,
    test: val => val.indexOf(stringToExclude) === -1,
    params: {
      // params are available for interpolation the default messages
      mustNotContain: stringToExclude
    }
  })
})

Your code can then be used as follows:

import { setLocale, string } from 'yup';
import 'your-yup-extension-library';

// set custom default messages - both for built-in validations and
// the ones from your extension
setLocale({
  mixed: {
    required: "please enter ${path}",
    mustNotContain: "your answer must not contain '${mustNotContain}'"
  }
});

// now you can use the default message from the locale...
string()
  .mustNotContain("foo")
  .validate("foobar") 
// ==> "your answer must not contain 'foo'"

// ...or supply your own as usual:
string()
  .mustNotContain("foo", "don't say foo")
  .validate("foobar") 
// ==> "don't say foo"

Reminder: Validation messages can also be functions

For fully dynamic control over the message, instead of setting it to a string, you can set it to a function that returns a string. yup will pass in an options object with the following entries:

• path,
• value,
• originalValue (before casts and transformations),
• label
• for custom tests, any values passed into the params option when the test was defined
• some built-in tests have additional parameters as well, check the yup documentation

(This is just part of the core yup library.)

yup-universal-locale will look up a matching message in the following order of preference:

1. The message supplied directly to the test method
2. The message matching the schema type and the test name in the locale
3. The message matching the test name in the mixed schema in the locale
4. The message set in the locale for mixed.default