NodeJS
The Importance of Custom Validators and How to Create Them
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In Node.js, validation is very important in ensuring that data remains intact and also protected. Even though libraries like express-validator are helpful, it is much easier to implement object-oriented validation with class-validator as it results in more organized, reusable, and clear codes. With class-validator, you can build validation logic in a clean and maintainable way since it works well with TypeScript and plain Javascript. Custom Validators: Their Need and Use
- Enhanced Organization: class-validator is a custom validator that uses decorators to apply validation, thereby following a neat object-oriented approach. This makes the code easier to read while simplifying complex validation logic.
- Reduced Code Redundancy: Properties and classes can share the same custom validators leading to reduced code duplication and improved maintenance.
- Simplified Error Messaging: Users are shielded from complex underlying error messages when custom validators are used.
- Enhanced Library Support: Other libraries such as class-transformer work hand in hand with class-validator to ensure that validating and transforming objects is perfected.
How to Create Custom Validators in Node.js with class-validator
1. Install Dependencies
Install class-validator and class-transformer (optional, for object transformation).
npm install class-validator class-transformer
2. Create a Custom Validator
A custom validator is a function that validates the data according to your logic. In order to build a custom validator, you have to use @ValidatorConstraint decorator to specify the rule and @Validate to apply the rule.
Here’s how to build custom email validator which verifies if email domain is:
@mydomain.com:import { ValidatorConstraint, ValidatorConstraintInterface, ValidationArguments, Validate } from 'class-validator';// Define the custom validator@ValidatorConstraint({ name: 'isEmailDomainValid', async: false })class IsEmailDomainValid implements ValidatorConstraintInterface { validate(email: string, args: ValidationArguments) { return email.endsWith('@mydomain.com'); // Check if email ends with '@mydomain.com' } defaultMessage(args: ValidationArguments) { return 'Email must be from the @mydomain.com domain'; }}// Decorator to use on the propertyexport function IsValidEmail() { return Validate(IsEmailDomainValid);}
3. Apply Custom Validator to a DTO (Data Transfer Object)
So, you have now applied the custom validator in a particular class like normally a DTO, which explains what structure the data that needs to be validated should have.
import { IsString, IsEmail, IsInt } from 'class-validator';class UserDTO { @IsString() @IsEmail() @IsValidEmail() // Applying the custom validator email: string; @IsInt() @Min(18) age: number;} Ready to transform your business with our technology solution? Contact Us today to Leverage Our NodeJS Expertise.
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