middleware-props

elegant way to consume middleware props in your routes

Problem

usually for express applications we attach some properties to req in middleware like req.user = user

// below middleware attaches user property to req
const authenticateUser = (req: Request, res: Response, next: NextFunction) => {
  try {
    const cookie = req.headers.cookie ?? '';
    const user = getCurrentUser(cookie);
    req.user = user;
    next();
  } catch (err) {
    next(err);
  }
};

// in subsequent middlewares and routes we can use req.user
app.get('/', authenticateUser, (req, res, next) => {
  try {
    const user = req.user;
    res.json(user);
  } catch (err) {
    next(err);
  }
});

but above method becomes complicated once we start having middleware chain and it becomes hard to track which middleware attached which properties

this package solves this problem

Usage

addProps and getProps methods

basic

import express, { NextFunction, Request, Response } from 'express';

import { addProps, getProps } from '../lib/methods';

namespace Middlewares {
  export type AuthenticateUser = {
    user: User;
  };
}

type User = {
  id: number;
  name: string;
};

const getCurrentUser = (cookie: string): User => {
  // some logic to get the user based on cookie
  const user = {
    name: 'Dummy',
    id: 12,
  };
  return user;
};

const authenticateUser = (req: Request, res: Response, next: NextFunction) => {
  try {
    const cookie = req.headers.cookie ?? '';
    const user = getCurrentUser(cookie);
    const props: Middlewares.AuthenticateUser = { user };
    addProps(req, props, 'authenticateUser');
    next();
  } catch (err) {
    next(err);
  }
};

const app = express();
app.use(express.json());
app.get('/', authenticateUser, (req, res, next) => {
  try {
    const { user } = getProps<Middlewares.AuthenticateUser>(
      req,
      'authenticateUser'
    );
    res.json(user);
  } catch (err) {
    next(err);
  }
});

const PORT = 8000;

app.listen(PORT, () => {
  console.log(`listening on http://localhost:${PORT}`);
});

using multiple middlewares

import express, { NextFunction, Request, Response } from 'express';

import { addProps, getProps } from '../lib/methods';

type User = {
  id: number;
  name: string;
};
type Role = 'guest' | 'user' | 'admin';

namespace Middlewares {
  export type AuthenticateUser = {
    user: User;
  };
  export type AttachRole = {
    role: Role;
  };
}

const getCurrentUser = (cookie: string): User => {
  // some logic to get the user based on cookie
  const user = {
    name: 'Dummy',
    id: 12,
  };
  return user;
};

const authenticateUser = (req: Request, res: Response, next: NextFunction) => {
  try {
    const cookie = req.headers.cookie ?? '';
    const user = getCurrentUser(cookie);
    const props: Middlewares.AuthenticateUser = { user };
    addProps(req, props, 'authenticateUser');
    next();
  } catch (err) {
    next(err);
  }
};

const getRole = (user: User): Role => {
  return 'admin';
};

/**
 *
 * dependencies: authenticateUser
 */
const attachRole = (req: Request, res: Response, next: NextFunction) => {
  try {
    // since attachRole middleware is used after authenticateUser middleware
    // we can use properties attached by authenticateUser middleware
    const { user } = getProps<Middlewares.AuthenticateUser>(
      req,
      'authenticateUser'
    );
    addProps<Middlewares.AttachRole>(
      req,
      {
        role: getRole(user),
      },
      'attachRole'
    );
    next();
  } catch (err) {
    next(err);
  }
};

const app = express();
app.use(express.json());
app.get('/', authenticateUser, attachRole, (req, res, next) => {
  try {
    const { user } = getProps<Middlewares.AuthenticateUser>(
      req,
      'authenticateUser'
    );
    const { role } = getProps<Middlewares.AttachRole>(req, 'attachRole');
    res.json({ user, role });
  } catch (err) {
    next(err);
  }
});

const PORT = 8000;

app.listen(PORT, () => {
  console.log(`listening on http://localhost:${PORT}`);
});

getAllProps method

const req = {
  body: {},
};

// inside first middleware
addProps<Middlewares.AuthenticateUser>(
  req,
  {
    user: {
      name: 'dummy',
      id: 1,
    },
  },
  'authenticateUser'
);

// inside second middlware
const { user: authenticatedUser } = getProps<Middlewares.AuthenticateUser>(
  req,
  'authenticateUser'
);
const getRole = (user: User): Role => {
  return 'admin';
};

addProps<Middlewares.AttachRole>(
  req,
  {
    role: getRole(authenticatedUser),
  },
  'attachRole'
);

const result = getAllProps(req);
/*
    {
      authenticateUser: { user: { name: 'dummy', id: 1 } },
      attachRole: { role: 'admin' },
    }
*/

More

visit samples directory https://github.com/rgsk/middleware-props/tree/main/src/samples

visit base.test.ts file to see advanced use-cases supported https://github.com/rgsk/middleware-props/blob/main/src/base.test.ts