joi

Object Schema Validation

This feature allows you to define a schema for an object, specifying the expected type of each property, and then validate data against this schema. The code sample demonstrates creating a schema for user data and validating an object against it.

{"const Joi = require('joi');\nconst schema = Joi.object({\n  username: Joi.string().alphanum().min(3).max(30).required(),\n  password: Joi.string().pattern(new RegExp('^[a-zA-Z0-9]{3,30}$')),\n  repeat_password: Joi.ref('password'),\n  access_token: [Joi.string(), Joi.number()],\n  birth_year: Joi.number().integer().min(1900).max(2013),\n  email: Joi.string().email({ minDomainSegments: 2, tlds: { allow: ['com', 'net'] } })\n}).with('username', 'birth_year');\n\nconst dataToValidate = {\n  username: 'abc',\n  birth_year: 1994,\n  email: 'test@example.com'\n};\n\nconst result = schema.validate(dataToValidate);\nconsole.log(result);"}

Type Casting

Joi can cast values to other types as part of the validation process. In this example, a string representing a number is cast to an actual number, and a string 'TRUE' is cast to a boolean true.

{"const Joi = require('joi');\nconst schema = Joi.object({\n  age: Joi.number().integer(),\n  active: Joi.string().trim().lowercase().valid('true', 'false').truthy('true').falsy('false').default(false).cast('boolean')\n});\n\nconst dataToValidate = {\n  age: '30',\n  active: 'TRUE'\n};\n\nconst result = schema.validate(dataToValidate, { convert: true });\nconsole.log(result.value); // { age: 30, active: true }"}

Custom Validation Messages

Joi allows you to specify custom validation messages for when data does not conform to the schema. This example shows how to set a custom message for a string that is too short.

{"const Joi = require('joi');\nconst schema = Joi.string().min(10).message('The string needs to be at least 10 characters long.');\n\nconst result = schema.validate('short');\nconsole.log(result.error); // Custom error message"}