diff --git a/index.js b/index.js
index b69c249..d89393a 100644
--- a/index.js
+++ b/index.js
@@ -1,35 +1,68 @@
 /* global MutationObserver */
 var document = require('global/document')
 var window = require('global/window')
-var watch = []
+var watch = Object.create(null)
+var KEY_ID = 'onloadid'
 
 if (window && window.MutationObserver) {
   var observer = new MutationObserver(function (mutations) {
     for (var i = 0; i < mutations.length; i++) {
-      var mutation = mutations[i]
-      var x, y
-      for (x = 0; x < mutation.addedNodes.length; x++) {
-        for (y = 0; y < watch.length; y++) {
-          if (watch[y][0] === mutation.addedNodes[x]) {
-            watch[y][1]()
-          }
-        }
-      }
-      for (x = 0; x < mutation.removedNodes.length; x++) {
-        for (y = 0; y < watch.length; y++) {
-          if (watch[y][0] === mutation.removedNodes[x]) {
-            watch[y][2]()
-            watch.splice(y, 1)
-          }
-        }
-      }
+      eachMutation(mutations[i].removedNodes, function (target) {
+        target[1]()
+      })
+      eachMutation(mutations[i].addedNodes, function (target) {
+        // TODO: Should queue functions to run, then run them all on setImmediate?
+        target[0]()
+      })
     }
   })
   observer.observe(document.body, {childList: true, subtree: true})
 }
 
-module.exports = function onload (el, l, u) {
-  l = l || function () {}
-  u = u || function () {}
-  watch.push([el, l, u])
+module.exports = function onload (el, on, off) {
+  on = on || function () {}
+  off = off || function () {}
+  var id
+  if (el.dataset && el.dataset[KEY_ID]) {
+    id = el.dataset[KEY_ID]
+  } else {
+    // TODO: Is there a better way to uniquely identify an element?
+    var caller = onload.caller.toString()
+    if (caller) {
+      id = hash(caller)
+    } else {
+      var err = new Error()
+      var lines = err.stack.split('\n')
+      for (var i = 0; i < lines.length; i++) {
+        if (lines[i].indexOf('onload') !== -1) {
+          id = lines[i + 1]
+          break
+        }
+      }
+      id = hash(id.replace(/^[\s\uFEFF\xA0]+|[\s\uFEFF\xA0]+$/g, ''))
+    }
+    el.dataset[KEY_ID] = id
+  }
+  // TODO: Should we allow multiple set per element?
+  watch[id] = [on, off]
+}
+
+function eachMutation (nodes, fn) {
+  for (var i = 0; i < nodes.length; i++) {
+    if (nodes[i].dataset && nodes[i].dataset[KEY_ID] && watch[nodes[i].dataset[KEY_ID]]) {
+      fn(watch[nodes[i].dataset[KEY_ID]])
+    }
+    if (nodes[i].childNodes.length > 0) {
+      eachMutation(nodes[i].childNodes, fn)
+    }
+  }
+}
+
+function hash (str) {
+  var res = 5381
+  var i = str.length
+  while (i) {
+    res = (res * 33) ^ str.charCodeAt(--i)
+  }
+  return res >>> 0
 }
diff --git a/package.json b/package.json
index bd829e5..849e3b2 100644
--- a/package.json
+++ b/package.json
@@ -33,6 +33,7 @@
     "standard": "^6.0.7",
     "tape": "^4.5.0",
     "testron": "^1.2.0",
-    "wzrd": "^1.3.1"
+    "wzrd": "^1.3.1",
+    "yo-yo": "^1.2.1"
   }
 }
diff --git a/test.js b/test.js
index a2304ee..83ab972 100644
--- a/test.js
+++ b/test.js
@@ -1,5 +1,6 @@
 var onload = require('./')
 var test = require('tape')
+var yo = require('yo-yo')
 
 test('onload/onunload', function (t) {
   t.plan(2)
@@ -34,3 +35,128 @@ test('nested', function (t) {
   e2.appendChild(e3)
   e2.removeChild(e3)
 })
+
+test('complex', function (t) {
+  t.plan(4)
+  var state = []
+
+  function button () {
+    var el = yo`<button>click</button>`
+    onload(el, function () {
+      state.push('on')
+    }, function () {
+      state.push('off')
+    })
+    return el
+  }
+
+  var root = yo`<div>
+    ${button()}
+  </div>`
+  document.body.appendChild(root)
+
+  runops([
+    function () {
+      t.deepEqual(state, ['on'], 'turn on')
+      state = []
+      root = yo.update(root, yo`<p>${button()}</p>`)
+    },
+    function () {
+      t.deepEqual(state, ['off', 'on'], 'turn off/on')
+      state = []
+      root = yo.update(root, yo`<p>removed</p>`)
+    },
+    function () {
+      t.deepEqual(state, ['off'], 'turn off')
+      state = []
+      var btn = button()
+      root = yo.update(root, yo`<p><div>${btn}</div></p>`)
+      root = yo.update(root, yo`<p>
+        <div>Updated</div>
+        <div>${btn}</div>
+      </p>`)
+    },
+    function () {
+      t.deepEqual(state, ['off', 'on'], 'turn off/on')
+    }
+  ], t.end)
+})
+
+test('complex nested', function (t) {
+  var state = []
+  function button () {
+    var el = yo`<button>click</button>`
+    onload(el, function () {
+      state.push('on')
+    }, function () {
+      state.push('off')
+    })
+    return el
+  }
+  function app (page) {
+    return yo`<div class="app">
+      <h1>Hello</h1>
+      ${page}
+    </div>`
+  }
+
+  var root = app(yo`<div>Loading...</div>`)
+  document.body.appendChild(root)
+
+  runops([
+    function () {
+      t.deepEqual(state, [], 'did nothing')
+      state = []
+      root = yo.update(root, app(yo`<div class="page">
+        ${button()}
+      </div>`))
+    },
+    function () {
+      t.deepEqual(state, ['on'], 'turn on')
+      state = []
+      root = yo.update(root, app(yo`<div class="page">
+        <h3>Another Page</h3>
+      </div>`))
+    },
+    function () {
+      t.deepEqual(state, ['off'], 'turn off')
+      state = []
+      root = yo.update(root, app(yo`<div class="page">
+        ${button()}
+        ${button()}
+      </div>`))
+    },
+    function () {
+      t.deepEqual(state, ['on', 'on'], 'turn 2 on')
+      state = []
+      root = yo.update(root, app(yo`<div class="page">
+        ${button()}
+        ${button()}
+      </div>`))
+    },
+    function () {
+      t.deepEqual(state, [], 'do nothing')
+      state = []
+      root = yo.update(root, app(yo`<div class="page">
+        ${button()}
+        <p>removed</p>
+      </div>`))
+    },
+    function () {
+      t.deepEqual(state, ['off'], 'turn 1 off')
+    }
+  ], t.end)
+})
+
+function runops (ops, done) {
+  function loop () {
+    var next = ops.shift()
+    if (next) {
+      next()
+      setTimeout(loop, 10)
+    } else {
+      done()
+    }
+  }
+  setTimeout(loop, 10)
+}