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 the following 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 value; // Return the value unchanged
};
        
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?

score 40 · Answer 1 · edited Jun 12 '23 at 22:35

40

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");
      }

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

edited Jun 12 '23 at 22:35

Mr.Singh

1,421
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answered May 06 '20 at 15:08

Muslem Omar

1,021
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12

1

Hmm, types say the 1st arg of `helper.message` needs to be `Record`, not `string`... – deb Jun 06 '21 at 14:39
3

You can ignore the type error... but I think it should return `value` instead of `true` at the end – Igorsvee Jul 10 '21 at 15:05
1

To fix type issue return `helper.message({custom: 'put error message here'})` – Peter Moses Sep 28 '21 at 04:54
3

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 – Overclocked Skid Mar 31 '22 at 03:27

score 34 · Accepted Answer · edited Jun 12 '23 at 07:21

34

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 the following 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 value; // Return the value unchanged
};

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]
    }
  ]
}

edited Jun 12 '23 at 07:21

Mr.Singh

1,421
6
21
46

answered Oct 17 '19 at 06:20

SuleymanSah

17,153
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@ShifutHossain I tried it and it gives the error [ValidationError]: "username" contains an invalid value] – SuleymanSah Oct 17 '19 at 06:45
https://codesandbox.io/s/billowing-leaf-zwo19?fontsize=14 I've also tried it here – Shifut Hossain Oct 17 '19 at 06:46
Did you try on your local computer? – SuleymanSah Oct 17 '19 at 06:48
@ShifutHossain as I know joi is not compatible in browser, can you check in your node application? – SuleymanSah Oct 17 '19 at 06:49
I added the output in to the answer, when used in a node app. Isn't it what you want? – SuleymanSah Oct 17 '19 at 06:52
Yeah, now it's working on node environment. It was my mistake I always use Codesandbox for practicing. – Shifut Hossain Oct 17 '19 at 06:53
In codesandbox there is template project for node apps, but I didn't tried. – SuleymanSah Oct 17 '19 at 06:55
Thanks, but how do you define a custom error text? – Slava Fomin II Nov 29 '21 at 21:55

Isaac · Answer 3 · 2020-10-07T06:24:52.787

2

This is how I validated my code, have a look at it and try to format yours

const busInput = (req) => {
  const schema = Joi.object().keys({
    routId: Joi.number().integer().required().min(1)
      .max(150),
    bus_plate: Joi.string().required().min(5),
    currentLocation: Joi.string().required().custom((value, helper) => {
      const coordinates = req.body.currentLocation.split(',');
      const lat = coordinates[0].trim();
      const long = coordinates[1].trim();
      const valRegex = /-?\d/;
      if (!valRegex.test(lat)) {
        return helper.message('Laltitude must be numbers');
      }
      if (!valRegex.test(long)) {
        return helper.message('Longitude must be numbers');
      }
    }),
    bus_status: Joi.string().required().valid('active', 'inactive'),
  });
  return schema.validate(req.body);
};

edited Oct 07 '20 at 06:24

answered Oct 06 '20 at 20:56

Isaac

37
3

6

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. – Hoppeduppeanut Oct 06 '20 at 22:05
First argument of the `message()` is `LanguageMessages` which is `Record`. – Slava Fomin II Nov 29 '21 at 21:57
you could validate currentLocation as an array of numbers – alex Jun 02 '22 at 18:15

How to add custom validator function in Joi?

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