Attempt at nodejs stdout "buffer interjection". Might be useful, ugly attempt though. Relies on ANSI escape codes (primarily SCP, RCP, ED). Suggestions welcome, cleanup even more welcome. Please note that some things were done for specific reasons however - overloading `process.stdout` methods was not possible in my attempts and resulted in erro…

interject.js

var readline = require('readline'),
	EventEmitter = require('events').EventEmitter,
	buffer = require('buffer')

var stdoutBuffer = new EventEmitter() // can't use util.inherits() with process.stdout. :\

for(x in process.stdout) stdoutBuffer[x] = process.stdout[x]
stdoutBuffer.last = ''

stdoutBuffer.write = function(input, encoding) {
	process.stdout.write(input, encoding)
	var miniBuffer = input.toString().replace('\r', '')
	miniBuffer = miniBuffer.split('\n')
	if(miniBuffer.length > 1) {
		stdoutBuffer.last = miniBuffer.pop()
	} else {
		stdoutBuffer.last += input.toString()
	}
}
stdoutBuffer.interject = function(input, encoding) {
	var last = this.last
	process.stdout.write("\u001b[u\u001b[0J")
	process.stdout.write(input, encoding)
	process.stdout.write("\n")
	process.stdout.write(last)
}
process.stdout.on('drain', function() { stdoutBuffer.emit('drain') })
process.stdout.on('error', function(error) { stdoutBuffer.writeable = false; stdoutBuffer.emit('error', error) })
process.stdout.on('close', function() { stdoutBuffer.writeable = false; stdoutBuffer.emit('close') })

rl = readline.createInterface({
	input:process.stdin,
	output:stdoutBuffer,
	terminal: true,
})

rl
	.on('line', function(line) {
		stdoutBuffer.write("\u001b[s")
		rl.prompt()
	})
	.on('close', function() {
    process.exit(0)
	})

stdoutBuffer.write("\u001b[s")
rl.prompt()

var i = 0
setInterval(function() {
	stdoutBuffer.interject('test ' + ++i)
}, 10 * 1000)

Note: use within tmux seems to cause a minor bug - or tmux has a bug itself in cursor positioning. Unknown whether it affects screen.

Confirmed to be a tmux bug: http://sourceforge.net/mailarchive/message.php?msg_id=28592212

filed; https://sourceforge.net/p/tmux/feature-requests/113/