Use-case

This utility is for the execution of arbitrarily complex express-style middleware.

Express middleware is executed by allowing either a middleware function or an array, calling each piece of middleware and awaiting the callback next to be invoked. When next is invoked, the next middleware is called. If next is invoked with an argument, this is treated as an error. Upon being invoked with an error, all subsequent middleware is ignored until an error handler middleware is encountered, defined as a piece of middleware expecting 4 arguments, rather than 3.

This, for example, is how error handling middleware looks:

(err, req, res, next) => {
  // Error handler
}

As compared to normal middleware, which would be skipped over if an error is being propagated through the middleware:

(req, res, next) => {
  // Normal middlware
}

Note that the names of the arguments don't matter, just the amount of expected arguments.

Usage

$ npm install execute-middleware

const executeMW = require('execute-middleware');

// Some middleware
const SOME_MIDDLEWARE = [
  (req, res, next) => {
    console.log('hi.');
    next()
  },
  [
    (req, res, next) => {
      console.log('hey');
    },
    (err, req, res, next) => {
      console.log('I will not be called, because im not an error.');
    }
  ]
];

// Execute MW serially
executeMW.serial(SOME_MIDDLEWARE);

// Execute MW concurrently
executeMW.concurrent(SOME_MIDDLEWARE);