express-harness

A fully typed, light-weight, unopinionated and no-dependencies Express.JS middleware that helps with the validation of requests.

In general, as a developer,

• You provide a validation schema that has the following attributes:

  • Where to look (query, body etc..)
  • What to look (field names)
  • Whether it's required or not
  • Defines your own validation logic against this field.

• This middleware will then validate the request with the schema, and if it fails, it'll return the request with 400 (by default).

Installation

npm i @wunderland/express-harness

or

yarn add @wunderland/express-harness

Examples

Basic Example

import { validateRequest } from "@wunderland/express-harness";
import express from "express";

const app = express();

app.post(
  "/",
  validateRequest({ body: { user_id: { required: true } } }),
  (request, response) => {
    return response.status(200).json({ user_id: request.body.user_id });
  }
);

Response

{
  "error": "Validation for the following fields are failed",
  "fields": {
    "body": {
      "user_id": "user_id is required"
    }
  }
}

Custom Validation

import { validateRequest } from "@wunderland/express-harness";
import express from "express";

const app = express();

app.post(
  "/",
  validateRequest({
    body: {
      user_id: {
        required: true,
      },
      age: {
        required: false,
        validator: (request) => {
          const {
            body: { age = 5 },
          } = request;
          if (Number(age) < 10) {
            return `You must be at least 10 years old`;
          }
          return undefined;
        },
      },
    },
  }),
  (request, response) => {
    return response.status(200).json({ user_id: request.body.user_id });
  }
);

Response

{
  "error": "Validation for the following fields are failed",
  "fields": {
    "body": {
      "age": "You must be at least 10 years old",
      "user_id": "user_id is required"
    }
  }
}

API

express-harness exports a named function:

validateRequest(schema, [options])

This validateRequest method will validate the express request against the specified schema and will return a 400 with a default error message (which is configurable through options).

schema

The schema is a normal Object that has the following type definition:

Validation Schema Type

type ValidateRequestSchema = {
  body?: {
    [key: string]: {
      required: boolean;
      validator?: ValidatorFunction;
    };
  };
  query?: {
    [key: string]: {
      required: boolean;
      validator?: ValidatorFunction;
    };
  };
  files?: {
    [key: string]: {
      required: boolean;
    };
  };
  params?: {
    [key: string]: {
      required: boolean;
      validator?: ValidatorFunction;
    };
  };
};

Custom Validation ( ValidatorFunction )

You can specify your own validation logic against the fields using this validator method.

When specified, this will be invoked with the following argument signature:

type ValidatorFunction = (request: Request) => string | undefined;

If this validator function returns a string, it'll be treated as an error, and the returned string will be used as the error message. If it's undefined, then it'll be considered as no-error.

options [object]

Through options, you can configure the HTTP Error Code and format the error response according to your needs. It also does the cleaning of saved files (through Multer) in case any of the validation fails (fail fast)

type ValidateRequestOptions = {
  errorCode: number;
  formatErrorPayload: (fields: Fields) => any;
  cleanupMulter: boolean;
};

cleanupMulter: [boolean] (defaults to true)

Delete the saved files (by multer) in case any validation fails.

errorCode [number] (defaults to 400)

The HTTP status code to return on error. You can set any number (although 400 is the preferred).

formatErrorPayload [function] (defaults to a built-in formatter)

This is a helper function that'll let you to customize the error response before sending it to the client.

When provided, this function will get invoked with an object as its param which has the following signature:

type Fields = {
  body: { [key: string]: string | undefined };
  query: { [key: string]: string | undefined };
  params: { [key: string]: string | undefined };
  files: { [key: string]: string | undefined };
};

Contribution

There's a pretty high-chance where we might've missed many issues. If you find one, please feel free to fork and submit a patch

License

This library is licensed under MIT