Add support for async middleware and handlers to Express

express-async.js

/**
 * Wrap an Express middleware or handler for async support.
 * @param {function} fn The middleware or handler to wrap
 * @returns {function} Wrapped function
 */
exports.wrap = function(fn) {
  if (fn.length === 4) {
    // Wrap error handler
    return (err, req, res, next) => {
      const r = fn(err, req, res, next)
      if (typeof r === 'object' && typeof r.catch === 'function') {
        r.catch(next)
      }
    }
  } else if (fn.length === 3) {
    // Wrap middleware; assumes middleware calls `next`
    return (req, res, next) => {
      const r = fn(req, res, next)
      if (typeof r === 'object' && typeof r.catch === 'function') {
        r.catch(next)
      }
    }
  } else if (fn.length === 2) {
    // Wrap a handler, calling `next` when it resolves
    return (req, res, next) => {
      const r = fn(req, res)
      if (typeof r === 'object' && typeof r.catch === 'function') {
        r.catch(next)
      }
    }
  } else {
    // Don't know what to do with this function; return as-is
    return fn
  }
}

/**
 * Hook into Express' Layer class to automatically wrap each handler
 */
exports.autoWrap = function() {
  const Layer = require('express/lib/router/layer')

  // Don't hook if already hooked
  if (!Layer.prototype.hasOwnProperty('handle')) {
    Object.defineProperty(Layer.prototype, 'handle', {
      get: function() {
        return this.__handle
      },
      set: function(fn) {
        this.__handle = exports.wrap(fn)
      }
    })
  }
}

/**
 * Decorate an Express App or Router with getAsync, postAsync, etc..
 * @param {Express.App|Express.Router} appOrRouter Express App or Router
 * @return {Express.App|Express.Router} same as appOrRouter
 */
exports.decorateApp = function(appOrRouter) {
  for (let verb of ['post', 'get', 'all', 'patch', 'use', 'head', 'option', 'put', 'delete']) {
    appOrRouter[verb + 'Async'] = function(route, ...handlers) {
      // eslint-disable-next-line security/detect-object-injection
      appOrRouter[verb].call(appOrRouter, route, ...handlers.map(exports.wrap))
    }
  }
  return appOrRouter
}