index.js

;(function () {

var ClassList = require("class-list")

function h() {
  var args = [].slice.call(arguments), e = null
  function item (l) {
    var r
    function parseClass (string) {
      var m = string.split(/([\.#]?[a-zA-Z0-9_-]+)/)
      m.forEach(function (v) {
        var s = v.substring(1,v.length)
        if(!v) return
        if(!e)
          e = document.createElement(v)
        else if (v[0] === '.')
          ClassList(e).add(s)
        else if (v[0] === '#')
          e.setAttribute('id', s)
      })
    }

    if(l == null)
      ;
    else if('string' === typeof l) {
      if(!e)
        parseClass(l)
      else
        e.appendChild(r = document.createTextNode(l))
    }
    else if('number' === typeof l
      || 'boolean' === typeof l
      || l instanceof Date
      || l instanceof RegExp ) {
        e.appendChild(r = document.createTextNode(l.toString()))
    }
    //there might be a better way to handle this...
    else if (Array.isArray(l))
      l.forEach(item)
    else if(l instanceof Node)
      e.appendChild(r = l)
    else if(l instanceof Text)
      e.appendChild(r = l)
    else if ('object' === typeof l) {
      for (var k in l) {
        if('function' === typeof l[k]) {
          if(/^on\w+/.test(k)) {
            e.addEventListener(k.substring(2), l[k])
          } else {
            e[k] = l[k]()
            l[k](function (v) {
              e[k] = v
            })
          }
        }
        else if(k === 'style') {
          for (var s in l[k]) (function(s, v) {
            if('function' === typeof v) {
              e.style.setProperty(s, v())
              v(function (val) {
                e.style.setProperty(s, val)
              })
            } else
              e.style.setProperty(s, l[k][s])
          })(s, l[k][s])
        } else
          e[k] = l[k]
      }
    } else if ('function' === typeof l) {
      //assume it's an observable!
      var v = l()
      e.appendChild(r = v instanceof Node ? v : document.createTextNode(v))

      l(function (v) {
        if(v instanceof Node && r.parentElement)
          r.parentElement.replaceChild(v, r), r = v
        else
          r.textContent = v
      })

    }

    return r
  }
  while(args.length)
    item(args.shift())

  return e
}

if(typeof module === 'object')
 module.exports = h
else
  this.hyperscript = h
})()