tessl/npm-express-validator

Express middleware for comprehensive request validation and sanitization.

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Overview

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Validation Chain Builders

Name: tessl/npm-express-validator
Author: tessl

Core functions for creating validation chains that target specific request locations. Each builder creates a validation chain that can be extended with validators and sanitizers.

Capabilities

Body Validation

Creates validation chains for fields in req.body.

/**
 * Creates validation chain for req.body fields
 * @param fields - Field name(s) to validate (supports nested paths and wildcards)
 * @param message - Default error message for failed validations
 * @returns ValidationChain for chaining validators and sanitizers
 */
function body(fields?: string | string[], message?: string): ValidationChain;

Usage Examples:

import { body } from "express-validator";

// Single field
body('email').isEmail();

// Multiple fields  
body(['name', 'email']).trim().notEmpty();

// Nested fields
body('user.profile.age').isInt({ min: 0 });

// Array elements
body('items.*.quantity').isInt({ min: 1 });

// With custom error message
body('password', 'Password must be at least 6 characters').isLength({ min: 6 });

Query Parameter Validation

Creates validation chains for fields in req.query.

/**
 * Creates validation chain for req.query fields
 * @param fields - Field name(s) to validate
 * @param message - Default error message for failed validations
 * @returns ValidationChain for chaining validators and sanitizers
 */
function query(fields?: string | string[], message?: string): ValidationChain;

Usage Examples:

import { query } from "express-validator";

// Query parameters
query('page').isInt({ min: 1 }).toInt();
query('limit').isInt({ min: 1, max: 100 }).toInt();
query('search').trim().escape();
query('sort').isIn(['name', 'date', 'price']);

URL Parameter Validation

Creates validation chains for fields in req.params.

/**
 * Creates validation chain for req.params fields
 * @param fields - Field name(s) to validate
 * @param message - Default error message for failed validations
 * @returns ValidationChain for chaining validators and sanitizers
 */
function param(fields?: string | string[], message?: string): ValidationChain;

Usage Examples:

import { param } from "express-validator";

// Route parameters
param('id').isUUID();
param('userId').isInt().toInt();
param('slug').isSlug();
param('category').isAlpha();

Header Validation

Creates validation chains for fields in req.headers.

/**
 * Creates validation chain for req.headers fields
 * @param fields - Field name(s) to validate
 * @param message - Default error message for failed validations
 * @returns ValidationChain for chaining validators and sanitizers
 */
function header(fields?: string | string[], message?: string): ValidationChain;

Usage Examples:

import { header } from "express-validator";

// Request headers
header('authorization').notEmpty().matches(/^Bearer .+/);
header('content-type').equals('application/json');
header('x-api-key').isUUID();

Cookie Validation

Creates validation chains for fields in req.cookies.

/**
 * Creates validation chain for req.cookies fields
 * @param fields - Field name(s) to validate
 * @param message - Default error message for failed validations
 * @returns ValidationChain for chaining validators and sanitizers
 */
function cookie(fields?: string | string[], message?: string): ValidationChain;

Usage Examples:

import { cookie } from "express-validator";

// Cookies
cookie('sessionId').isUUID();
cookie('preferences').isJSON();
cookie('theme').isIn(['light', 'dark']);

Universal Field Validation

Creates validation chains that check all request locations (body, cookies, headers, params, query).

/**
 * Creates validation chain that checks all request locations
 * @param fields - Field name(s) to validate
 * @param message - Default error message for failed validations
 * @returns ValidationChain for chaining validators and sanitizers
 */
function check(fields?: string | string[], message?: string): ValidationChain;

Usage Examples:

import { check } from "express-validator";

// Checks all locations for 'id' field
check('id').isUUID();

// Useful when field could be in multiple locations
check('token').notEmpty();

Custom Location Builder

Creates validation chain builders for specific location combinations.

/**
 * Creates custom check function for specific locations
 * @param locations - Array of locations to check
 * @returns Function that creates ValidationChain for specified locations
 */
function buildCheckFunction(locations: Location[]): 
  (fields?: string | string[], message?: string) => ValidationChain;

Usage Examples:

import { buildCheckFunction } from "express-validator";

// Custom builder for body and query only
const checkBodyAndQuery = buildCheckFunction(['body', 'query']);

// Use the custom builder
checkBodyAndQuery('searchTerm').trim().notEmpty();

Chain Methods

All validation chain builders return a ValidationChain that supports:

interface ValidationChain {
  // Conditional validation
  if(condition: (value: any, meta: Meta) => boolean): ValidationChain;
  optional(options?: { nullable?: boolean; checkFalsy?: boolean }): ValidationChain;
  
  // Error handling
  withMessage(message: string): ValidationChain;
  bail(): ValidationChain;
  
  // Negation
  not: ValidationChain;
  
  // Skip options
  skipUndefined(): ValidationChain;
  skipNull(): ValidationChain;
  skipEmpty(): ValidationChain;
}

Field Path Syntax

Express-validator supports flexible field path syntax:

Simple fields: 'name', 'email'
Nested objects: 'user.profile.name', 'settings.theme.mode'
Array elements: 'items.0.name', 'users.1.email'
Wildcards: 'items.*.quantity' (matches any array index)
Multiple fields: ['name', 'email'] (validates both fields with same rules)

Examples:

// Nested object validation
body('user.profile.bio').isLength({ max: 500 });

// Array validation
body('products.*.price').isDecimal({ decimal_digits: '2' });

// Multiple field validation
body(['firstName', 'lastName']).trim().notEmpty();