overshadow-listeners

#overshadow-listeners

Add an event listener before existing listeners.

Why

Event listeners always fire in the order they are added, yet sometimes we have no control over this ordering and require certain listeners to definitely run before any others.

Example

var http = require('http')
var Overshadow = require('overshadow-listeners')

var server = http.createServer(function(req, res) {
  res.end('ok!')
})

Overshadow(server).on('request', function(req, res) {
  // This handler runs before any other request handlers
  // (including the handler supplied to http.createServer!)
  if (req.url !== '/') return res.end('no.') // reject any requests other than those for '/'
})

Overshadow(server).once('request', function(req, res) {
  // happens only once, before any other request handlers
})

server.listen(9000)

detach/reattach

Alternatively, manually detach and reattach listeners:

var overshadow = Overshadow(server)
overshadow.detach('request')

// attach whatever listeners you need
server.on('request', function(req, res) {
  if (req.url !== '/') return res.end('no.')
})

overshadow.reattach('request')
// remember to reattach old listeners

detach/reattach is chainable

We've included a simple .then(fn) method you can call to make chainable the process of detaching, doing something then reattaching. .then(fn) does nothing but execute the supplied function

Overshadow(server)
.detach('request')
.then(function() { // '.then' executes supplied fn & returns chain 
  server.once('request', function(req, res) {
    if (req.url !== '/') return res.end('no.')
  })
})
.reattach('request') // remember to reattach old listeners

Also See

• hughsk/on-first

Licence

MIT