connect-composer

v1.0.0

Published

2 years ago

Connect and reuse connect middlewares

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commenthol

compose connect express middleware pipeline

connect-composer

Connect and reuse connect/ express middlewares

Compose connect/ express compatible middlewares and reuse or extend them.

Features:

Stack middlewares
Use connect middlewares without or with connect, express
Trap errors within middlewares using function (err, req, res, next) functions
Safely catch errors within middlewares
Modify and reuse existing middlewares

Description

Stack Middlewares

This module allows to join middlewares together:

var compose = require('connect-composer')
var req = { test: [] }
var res = {}
var middlewares1 = [
  function (req, res, next) { req.test.push('one'); next() },
  function (req, res, next) { req.test.push('two'); next() }
]
var middlewares2 = [
  function (req, res, next) { req.test.push('three'); next() },
  function (req, res, next) { req.test.push('four'); next() }
]
// create a new middleware
var newMiddlewares = compose(middlewares1, middlewares2)
// run new composed middleware
newMiddlewares(req, res, function () {
  console.log(req.test) // < [ 'one', 'two', 'three', 'four' ]
})

Stack composed middlewares

You can also stack composed middlewares:

var compose = require('connect-composer')
var req = { test: [] }
var res = {}
// pass as Array
var middlewares1 = compose([
  function (req, res, next) { req.test.push('one'); next() },
  function (req, res, next) { req.test.push('two'); next() }
])
// or by Argument
var newMiddlewares = compose(
  middlewares1,
  function (req, res, next) { req.test.push('three'); next() },
  function (req, res, next) { req.test.push('four'); next() }
)
// run new composed middleware
newMiddlewares(req, res, function () {
  console.log(req.test) // < [ 'one', 'two', 'three', 'four' ]
})

Trap and catch errors

Traps errors and catches errors within middlewares (prevents server from crashing)

var compose = require('connect-composer')
var req = { test: [] }
var res = {}
var middlewares = compose(
  function (req, res, next) { req.test.push('one'); next() },
  function (req, res, next) {
    next('badly')           // middleware calls `next` with error parameter
  },
  function (req, res, next) {
    req.test.push('two')    // is never called
    next()
  },
  function (err, req, res, next) { // error is trapped here; function has arity 4
    console.log(err + ' trapped')  // < badly trapped
    next()                  // continue with the processing
  },
  function (req, res, next) { req.test.push('three'); next() },
  function (req, res, next) {
    if (1) throw new Error('another error') // middleware calls `next` with error parameter
    next()
  },
  function (req, res, next) {
    req.test.push('four')   // is never called
    next()
  }
)
// run new composed middleware
middlewares(req, res, function (err) {
  console.log(err)      // < [Error: another error] is catched
  console.log(req.test) // < [ 'one', 'three' ]
})

Manipulate and reuse middlewares

Use the following methods to change an existing composed middleware

unshift(middlewares) prepend middlewares to the front of the stack
push(middlewares) push middlewares to the end of the stack
before(selector, middlewares) insert middlewares before selector
after(selector, middlewares) insert middlewares after selector
replace(selector, middlewares) replace middlewares with name selector with middlewares
remove(selector) remove middlewares with name selector
clone() clone composed middlewares

var compose = require('connect-composer')
var res = {}
var initial = {
  two: function (req, res, next) { req.test.push('two'); next() },
  four: function (req, res, next) { req.test.push('four'); next() }
}
var others = {
  one: function one (req, res, next) { req.test.push('one'); next() },
  three: function three (req, res, next) { req.test.push('three'); next() },
  five: function othersFive (req, res, next) { req.test.push('five'); next() },
  six: function six (req, res, next) { req.test.push('six'); next() },
  seven: { seven: function (req, res, next) { req.test.push('seven'); next() } },
  eight: function (req, res, next) { req.test.push('eight'); next() }
}
// create a composed middleware
var composed = compose(initial)

// do some manipulation
composed.unshift(others.one)              // prepend
composed.push(others.five)                // append
composed.before('four', others.three)     // insert before
composed.after('othersFive', others.six)  // insert after
composed.after('six', others.seven)

// named functions become named middleware functions
console.log(composed.stack) // [ { one: [Function: one] },
                            //   { two: [Function] },
                            //   { three: [Function: three] },
                            //   { four: [Function] },
                            //   { othersFive: [Function: othersFive] },
                            //   { six: [Function: six] },
                            //   { seven: [Function] } ]

// lets clone the middlewares
var composed2 = composed.clone() // clone the middlewares; same as `compose(composed)`
composed2.remove('six').remove('two').remove('four') // remove middlewares

// do some more manipulation
composed.replace('seven', others.eight)   // replace middleware seven with eight

// run new composed middleware
var req = { test: [] }
composed(req, res, function () {
  console.log(4, req.test) // < [ 'one', 'two', 'three', 'four', 'five', 'six', 'eight' ]
})

// run the other composed middleware (with a different request)
var req2 = { test: [] }
composed2(req2, res, function () {
  console.log(5, req2.test) // < [ 'one', 'three', 'five', 'seven' ]
})

Example

Run the examples above with node test/sample.js.