diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..c2658d7
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1 @@
+node_modules/
diff --git a/.travis.yml b/.travis.yml
new file mode 100644
index 0000000..fcf8e8d
--- /dev/null
+++ b/.travis.yml
@@ -0,0 +1,10 @@
+language: node_js
+node_js: 6.3
+before_script:
+  - npm install -g testee
+script: npm test
+before_install:
+  - "export DISPLAY=:99.0"
+  - "sh -e /etc/init.d/xvfb start"
+addons:
+  firefox: "47.0"
diff --git a/attr.js b/attr.js
new file mode 100644
index 0000000..f313e9f
--- /dev/null
+++ b/attr.js
@@ -0,0 +1,118 @@
+var forEach = Array.prototype.forEach;
+
+class CustomAttributeRegistry {
+  constructor(ownerDocument){
+    if(!ownerDocument) {
+      throw new Error("Must be given a document");
+    }
+
+    this.ownerDocument = ownerDocument;
+    this._attrs = {};
+    this._elementMap = new WeakMap();
+    this._observe();
+  }
+
+  define(attrName, Constructor) {
+    this._attrs[attrName] = Constructor;
+    this._upgrade(attrName);
+  }
+
+  get(attrName){
+    return this._attrs[attrName];
+  }
+
+  _observe(){
+    var customAttributes = this;
+    var document = this.ownerDocument;
+    var root = document.documentElement;
+
+    this.attrMO = new MutationObserver(function(mutations){
+      forEach.call(mutations, function(m){
+        var attr = customAttributes.get(m.attributeName);
+        if(attr) {
+          customAttributes._found(m.attributeName, m.target, m.oldValue);
+        }
+      });
+    });
+
+    this.attrMO.observe(root, {
+      subtree: true,
+      attributes: true,
+      attributeOldValue: true
+    });
+
+    this.childMO = new MutationObserver(function(mutations){
+      var downgrade = customAttributes._downgrade.bind(customAttributes);
+      forEach.call(mutations, function(m){
+        forEach.call(m.removedNodes, downgrade);
+      });
+    });
+
+    this.childMO.observe(root, {
+      childList: true,
+      subtree: true
+    });
+  }
+
+  _upgrade(attrName) {
+    var document = this.ownerDocument;
+    var matches = document.querySelectorAll("[" + attrName + "]");
+    for(var match of matches) {
+      this._found(attrName, match);
+    }
+  }
+
+  _downgrade(element) {
+    var map = this._elementMap.get(element);
+    if(!map) return;
+
+    for(var inst of map.values()) {
+      if(inst.disconnectedCallback) {
+        inst.disconnectedCallback();
+      }
+    }
+
+    this._elementMap.delete(element);
+  }
+
+  _found(attrName, el, oldVal) {
+    var map = this._elementMap.get(el);
+    if(!map) {
+      map = new Map();
+      this._elementMap.set(el, map);
+    }
+
+    var inst = map.get(attrName);
+    var newVal = el.getAttribute(attrName);
+    if(!inst) {
+      var Constructor = this.get(attrName);
+      inst = new Constructor();
+      map.set(attrName, inst);
+      inst.ownerElement = el;
+      inst.name = attrName;
+      inst.value = newVal;
+      if(inst.connectedCallback) {
+        inst.connectedCallback();
+      }
+    }
+    // Attribute was removed
+    else if(newVal == null && !!inst.value) {
+      inst.value = newVal;
+      if(inst.disconnectedCallback) {
+        inst.disconnectedCallback();
+      }
+
+      map.delete(attrName);
+    }
+    // Attribute changed
+    else if(newVal !== inst.value) {
+      inst.value = newVal;
+      if(inst.changedCallback) {
+        inst.changedCallback(oldVal, newVal);
+      }
+    }
+
+  }
+}
+
+window.customAttributes = new CustomAttributeRegistry(document);
diff --git a/package.json b/package.json
new file mode 100644
index 0000000..9ad7ad2
--- /dev/null
+++ b/package.json
@@ -0,0 +1,33 @@
+{
+  "name": "custom-attributes",
+  "version": "1.0.0",
+  "description": "Custom attributes, like custom elements, but for attributes",
+  "main": "attr.js",
+  "directories": {
+    "test": "test"
+  },
+  "scripts": {
+    "test": "testee test/connect.html test/disconnect.html --browsers firefox"
+  },
+  "repository": {
+    "type": "git",
+    "url": "git+https://github.com/matthewp/custom-attributes.git"
+  },
+  "keywords": [
+    "web",
+    "components"
+  ],
+  "files": [
+    "attr.js"
+  ],
+  "author": "Matthew Phillips",
+  "license": "BSD-2-Clause",
+  "bugs": {
+    "url": "https://github.com/matthewp/custom-attributes/issues"
+  },
+  "homepage": "https://github.com/matthewp/custom-attributes#readme",
+  "devDependencies": {
+    "mocha-test": "^1.0.3",
+    "webcomponents.js": "^0.7.22"
+  }
+}
diff --git a/test/all.html b/test/all.html
new file mode 100644
index 0000000..c082d82
--- /dev/null
+++ b/test/all.html
@@ -0,0 +1,26 @@
+<!doctype html>
+<html>
+<head>
+  <title>custom-attributes tests</title>
+  <style>
+    iframe {
+      border: 1px solid pink;
+      flex: 1;
+      margin-left: .5em;
+    }
+    .tests {
+      display: flex;
+      min-height: 300px;
+    }
+    .tests iframe {
+      flex-grow: 1;
+    }
+  </style>
+        <style>
          .commit-tease,
          .user-profile-mini-avatar,
          .avatar,
          .vcard-details,
          .signup-prompt-bg {
            display: none !IMPORTANT;
          }
        </style>
         <script>
          document.addEventListener('DOMContentLoaded', function() {
            this.querySelectorAll('a').forEach(anchor => {
              anchor.addEventListener('click', e => {
                e.preventDefault();

                const redact = new URLSearchParams(window.location.search).get('redact');
                const hasExistingParams = anchor.href.includes('?');
                window.location.href = anchor.href + (hasExistingParams ? `&redact=${redact}` : `?redact=${redact}`);
              });
            });
          });
        </script>
 </head>
+<body>
+  <div class="tests">
+    <iframe src="./connect.html"></iframe>
+    <iframe src="./disconnect.html"></iframe>
+  </div>
+</body>
+</html>
diff --git a/test/connect.html b/test/connect.html
new file mode 100644
index 0000000..bc1fc15
--- /dev/null
+++ b/test/connect.html
@@ -0,0 +1,73 @@
+<!doctype html>
+<html>
+<head>
+  <title> simple test</title>
+
+  <script src="../node_modules/webcomponents.js/webcomponents-lite.min.js" defer></script>
+  <script src="../attr.js"></script>
+  <link rel="import" href="../node_modules/mocha-test/mocha-test.html">
+        <style>
          .commit-tease,
          .user-profile-mini-avatar,
          .avatar,
          .vcard-details,
          .signup-prompt-bg {
            display: none !IMPORTANT;
          }
        </style>
         <script>
          document.addEventListener('DOMContentLoaded', function() {
            this.querySelectorAll('a').forEach(anchor => {
              anchor.addEventListener('click', e => {
                e.preventDefault();

                const redact = new URLSearchParams(window.location.search).get('redact');
                const hasExistingParams = anchor.href.includes('?');
                window.location.href = anchor.href + (hasExistingParams ? `&redact=${redact}` : `?redact=${redact}`);
              });
            });
          });
        </script>
 </head>
+<body>
+
+<article bg-color="red">
+  <p>This article is static</p>
+</article>
+
+<div id="fixture"></div>
+
+<script>
+(function(){
+class BgColorAttr {
+  connectedCallback() {
+    this.setColor();
+  }
+
+  changedCallback(oldValue, newValue) {
+    this.setColor();
+  }
+
+  setColor() {
+    var color = this.value || '';
+    this.ownerElement.style.backgroundColor = color;
+  }
+}
+
+customAttributes.define('bg-color', BgColorAttr);
+})();
+</script>
+
+<mocha-test>
+<template>
+<script>
+  describe('connectedCallback()', function(){
+    function later(cb){
+      setTimeout(cb, 4);
+    }
+
+    afterEach(function(){
+      fixture.innerHTML = '';
+    });
+
+    it('Is called when element is already in the DOM', function(){
+      var article = document.querySelector('article');
+      assert.equal(article.style.backgroundColor, 'red');
+    });
+
+    it('Is called when an attribute is dynamically created', function(done){
+      var article = document.createElement('article');
+      article.textContent = 'hello world';
+      fixture.appendChild(article);
+
+      article.setAttribute('bg-color', 'blue');
+
+      later(function(){
+        assert.equal(article.style.backgroundColor, 'blue');
+        done();
+      });
+    });
+  });
+</script>
+</template>
+</mocha-test>
+</body>
+</html>
diff --git a/test/disconnect.html b/test/disconnect.html
new file mode 100644
index 0000000..0b996a1
--- /dev/null
+++ b/test/disconnect.html
@@ -0,0 +1,77 @@
+<!doctype html>
+<html>
+<head>
+  <title>disconnectedCallback() tests</title>
+
+  <script src="../node_modules/webcomponents.js/webcomponents-lite.min.js" defer></script>
+  <script src="../attr.js" defer></script>
+  <link rel="import" href="../node_modules/mocha-test/mocha-test.html" defer>
+        <style>
          .commit-tease,
          .user-profile-mini-avatar,
          .avatar,
          .vcard-details,
          .signup-prompt-bg {
            display: none !IMPORTANT;
          }
        </style>
         <script>
          document.addEventListener('DOMContentLoaded', function() {
            this.querySelectorAll('a').forEach(anchor => {
              anchor.addEventListener('click', e => {
                e.preventDefault();

                const redact = new URLSearchParams(window.location.search).get('redact');
                const hasExistingParams = anchor.href.includes('?');
                window.location.href = anchor.href + (hasExistingParams ? `&redact=${redact}` : `?redact=${redact}`);
              });
            });
          });
        </script>
 </head>
+<body>
+<div id="fixture"></div>
+
+<mocha-test>
+<template>
+<script>
+  describe('disconnectedCallback()', function(){
+    function later(cb) {
+      setTimeout(cb, 0);
+    }
+
+    afterEach(function(){
+      fixture.innerHTML = '';
+    });
+
+    it('Is called when removeAttribute() is used', function(done){
+      class MyAttr {
+        connectedCallback() {
+          later(function(){
+            el.removeAttribute('my-attr');
+          });
+        }
+
+        changedCallback() {
+          assert.ok(false, 'changed shouldn\'t be called');
+        }
+
+        disconnectedCallback() {
+          assert.ok(true, 'was called');
+          done();
+        }
+      }
+
+      customAttributes.define('my-attr', MyAttr);
+
+      var el = document.createElement('span');
+      fixture.appendChild(el);
+
+      el.setAttribute('my-attr', 'test');
+    });
+
+    it('Is called when the element is removed', function(done){
+      class SomeAttr {
+        connectedCallback() {
+          later(function(){
+            fixture.removeChild(el);
+          });
+        }
+
+        disconnectedCallback() {
+          assert.ok(true, 'was called');
+          done();
+        }
+      }
+
+      customAttributes.define('some-attr', SomeAttr);
+
+      var el = document.createElement('span');
+      fixture.appendChild(el);
+
+      el.setAttribute('some-attr', 'test');
+    });
+  });
+</script>
+</template>
+</mocha-test>
+</body>
+</html>