express-validator-schema-inference

TypeScript type helper to infer the resulting data type from an express-validator schema.

This utility allows you to statically infer the shape of validated request data, improving type safety and developer experience in Express projects using express-validator.

Features

• Infers nested object and array types from express-validator schema keys (e.g., user.name.first, user.phones.*.number).
• Supports common express-validator options (see below).

Supported schema options

The following express-validator schema options are currently supported for type inference:

Validators

• isBoolean
• isDate
• isFloat
• isInt
• isString
• isULID
• isAlpha
• isAlphanumeric
• isAscii
• isBase32
• isBase58
• isBase64
• isBtcAddress
• isCreditCard
• isCurrency
• isEmail
• isISO6346
• isISO4217
• isISO8601
• isObject
• notEmpty
• isEmpty
• isNumeric
• isJSON
• isURL
• isUUID
• isMobilePhone
• isLength
• contains
• equals
• matches
• isIP
• isHexadecimal
• isMongoId
• isMD5
• isDecimal
• isEthereumAddress
• isFQDN
• isHash
• isHexColor
• isIBAN
• isISBN
• isISSN
• isISIN
• isJWT
• isLatLong
• isLocale
• isLowercase
• isMimeType
• isPassportNumber
• isPort
• isPostalCode
• isRFC3339
• isSemVer
• isSlug
• isUppercase
• isDataURI
• isMagnetURI
• isMailtoURI
• isMACAddress
• isOctal
• isRgbColor
• isTime
• isVAT
• isWhitelisted
• isArray
• isIn

Sanitizers

• toBoolean
• toDate
• toFloat
• toInt
• ltrim
• rtrim
• trim
• toLowerCase
• toUpperCase
• escape
• unescape
• blacklist
• whitelist
• normalizeEmail
• stripLow
• toArray

Special options

• optional (marks a field as optional, reflected in the output type)
• custom (supports custom validators with type guards and assertions)
• customSanitizer (supports custom sanitizers with return type inference)

Other options may be partially supported if they do not affect the output type. See Limitations below for unsupported or advanced features.

Limitations

• Recursive fields using **.field (double star for deep/recursive matching) are not supported.
• Multiple custom validators/sanitizers using arbitrary keys (as described in the express-validator documentation) are not supported. Only single custom and customSanitizer properties are supported per field.
• Not all express-validator features are supported. Please see the source or open an issue if you need support for additional features.

Install

npm install --save-dev express-validator-schema-inference

Usage example

import type { Request, Response } from 'express';
import type { Schema } from 'express-validator';
import type { Infer } from 'express-validator-schema-inference';

function makeController<T extends Schema>(
  schema: T,
  handler: (req: Request & { data: Infer<T> }, res: Response) => any
) {
  // You should implement makeController so that req.data is set to the return value of matchedData.
}

makeController(
  {
    'user.name.first': {
      isString: true,
      trim: true,
    },
    'user.name.last': {
      isString: true,
      trim: true,
    },
    'user.emails': {
      isArray: true,
      isEmail: true,
    },
    'user.phones': {
      isArray: true,
      optional: true,
    },
    'user.phones.*.number': {
      isNumeric: true,
      trim: true,
    },
    'user.phones.*.code': {
      isNumeric: true,
      trim: true,
    },
    'user.age': {
      isInt: true,
      toInt: true,
    },
    role: {
      isIn: { options: [['owner', 'admin', 'user'] as const] },
      optional: { options: { values: 'null' } },
    },
  },
  (req, res) => {
    req.data;
    // {
    //   user: {
    //     name: {
    //       first: string;
    //       last: string;
    //     }
    //     emails: string[];
    //     phones: {
    //      number: string;
    //      code: string;
    //     }[] | undefined;
    //     age: number;
    //   }
    //   role: "owner" | "admin" | "user" | undefined | null;
    // }
  }
);

License

MIT License