index.js

header.js

var Nanocomponent = require('nanocomponent')
var html = require('choo/html')

class Header extends Nanocomponent {
	constructor () {
		super ()
		this.state = null
		this.emit = null
	}

	createElement(state, emit, black='') {
		console.log('render')
		this.state = state
		this.emit = emit
		return html`
			<header class='${black} psf z4 x xjb w100 px2 py1'>
			   header
			</header>
		`
	}

	update (newState, emit) {
    
		if (emit != this.emit) {
			this.state = newState
			this.emit = emit
			return true
		} else {
			return false
		}
    
	}
}

module.exports = Header

home.js

var html = require('choo/html')

var Header = require('./header.js')
var header = new Header()

module.exports = function (state, emitter) {

  return html`
	<main class="ffsans">
		${header.render(state, emitter)}
    		Home
	</main>
	`
}

index.js

var choo = require('choo')
var html = require('choo/html')

var home = require('./home.js')
var post = require('./post-view.js')

app.route('/', home)
app.route('/*', post)

var tree = app.start()
document.body.appendChild(tree)

post-view.js

var html = require('choo/html')

var Header = require('./header.js')
var header = new Header()

module.exports = function (state, emitter) {

  return html`
	<main class="ffsans">
		${header.render(state, emitter)}
    		Post
	</main>
	`
}

Did you figure it out? You can crate one instance and share it between views, or you can create an instance for each view.

https://github.com/hypermodules/hyperamp/blob/master/renderer/pages/main/index.js
https://github.com/hypermodules/hyperamp/blob/master/renderer/pages/preferences/index.js

It should work either way. The only restriction on modules is that you shouldn't use an instance in more on than once place at a time in the DOM.

Also you probably want to update based on state, not emitter. The emitter doesn't change between renders iirc. Neither does the state object instance. You should be comparing data and not top level object references.

https://gist.github.com/siiiick/f60760c675f08bba1f9ebba6ef0e7ae3#file-header-js-L24