How to add custom validator function in Joi?

Question

I have Joi schema and want to add a custom validator for validating data which isn't possible with default Joi validators.

Currently, I'm using the version 16.1.7 of Joi

   const method = (value, helpers) => {
      // for example if the username value is (something) then it will throw an error with flowing message but it throws an error inside (value) object without error message. It should throw error inside the (error) object with a proper error message

      if (value === "something") {
        return new Error("something is not allowed as username");
      }

      // Return the value unchanged
      return value;
    };

    const createProfileSchema = Joi.object().keys({
      username: Joi.string()
        .required()
        .trim()
        .empty()
        .min(5)
        .max(20)
        .lowercase()
        .custom(method, "custom validation")
    });

    const { error,value } = createProfileSchema.validate({ username: "something" });

    console.log(value); // returns {username: Error}
    console.log(error); // returns undefined

But I couldn't implement it the right way. I read Joi documents but it seems a little bit confusing to me. Can anyone help me to figure it out?

Solution 1

Your custom method must be like this:

const method = (value, helpers) => {
  // for example if the username value is (something) then it will throw an error with flowing message but it throws an error inside (value) object without error message. It should throw error inside the (error) object with a proper error message

  if (value === "something") {
    return helpers.error("any.invalid");
  }

  // Return the value unchanged
  return value;
};

Docs:

https://github.com/hapijs/joi/blob/master/API.md#anycustommethod-description

Output for value :

{ username: 'something' }

Output for error:

[Error [ValidationError]: "username" contains an invalid value] {
  _original: { username: 'something' },
  details: [
    {
      message: '"username" contains an invalid value',
      path: [Array],
      type: 'any.invalid',
      context: [Object]
    }
  ]
}

Solution 2

const Joi = require('@hapi/joi');

Joi.object({
    password: Joi
        .string()
        .custom((value, helper) => {

            if (value.length < 8) {
                return helper.message("Password must be at least 8 characters long")

            } else {
                return true
            }

        })

}).validate({
    password: '1234'
});

Comments

[SuleymanSah]

@ShifutHossain I tried it and it gives the error [ValidationError]: "username" contains an invalid value]

[Shifut Hossain]

codesandbox.io/s/billowing-leaf-zwo19?fontsize=14 I've also tried it here

[SuleymanSah]

Did you try on your local computer?

[SuleymanSah]

@ShifutHossain as I know joi is not compatible in browser, can you check in your node application?

[SuleymanSah]

I added the output in to the answer, when used in a node app. Isn't it what you want?

[Shifut Hossain]

Yeah, now it's working on node environment. It was my mistake I always use Codesandbox for practicing.

[SuleymanSah]

In codesandbox there is template project for node apps, but I didn't tried.

[Hoppeduppeanut]

While this might answer the question, if possible you should edit your answer to include an explanation of how this code block answers the question. This helps to provide context and makes your answer much more useful to future readers.

[deb]

Hmm, types say the 1st arg of helper.message needs to be Record<string, string>, not string...

[Igorsvee]

You can ignore the type error... but I think it should return value instead of true at the end

[Peter Moses]

To fix type issue return helper.message({custom: 'put error message here'})

[Slava Fomin II]

Thanks, but how do you define a custom error text?

[Slava Fomin II]

First argument of the message() is LanguageMessages which is Record<string, string>.

[Overclocked Skid]

You don't really need an else statement if you are returning in the if clause, though I recommend commenting and // else to improve readability

[alex]

you could validate currentLocation as an array of numbers