diff --git a/README.md b/README.md
index a850d69..4580c34 100644
--- a/README.md
+++ b/README.md
@@ -7,7 +7,7 @@ This module provides an efficient queue capable of managing thousands of concurr
 If you use NPM, `npm install d3-timer`. Otherwise, download the [latest release](https://github.com/d3/d3-timer/releases/latest). The released bundle supports AMD, CommonJS, and vanilla environments. Create a custom build using [Rollup](https://github.com/rollup/rollup) or your preferred bundler. You can also load directly from [d3js.org](https://d3js.org):
 
 ```html
-<script src="https://d3js.org/d3-timer.v0.1.min.js"></script>
+<script src="https://d3js.org/d3-timer.v0.2.min.js"></script>
 ```
 
 In a vanilla environment, a `d3_timer` global is exported. [Try d3-timer in your browser.](https://tonicdev.com/npm/d3-timer)
@@ -55,16 +55,12 @@ If [timer](#timer) is called within the callback of another timer, the new timer
 
 <a name="timer_restart" href="#timer_restart">#</a> <i>timer</i>.<b>restart</b>(<i>callback</i>[, <i>delay</i>[, <i>time</i>]])
 
-Restart a timer with the specified *callback* and optional *delay* and *time*. This is equivalent to stopping this timer and creating a new timer with the specified arguments, although this timer retains the original [id](#timer_id) and invocation priority.
+Restart a timer with the specified *callback* and optional *delay* and *time*. This is equivalent to stopping this timer and creating a new timer with the specified arguments, although this timer retains the original invocation priority.
 
 <a name="timer_stop" href="#timer_stop">#</a> <i>timer</i>.<b>stop</b>()
 
 Stops this timer, preventing subsequent callbacks. This method has no effect if the timer has already stopped.
 
-<a name="timer_id" href="#timer_id">#</a> <i>timer</i>.<b>id</b>
-
-An opaque, unique identifier for this timer.
-
 <a name="timerOnce" href="#timerOnce">#</a> d3.<b>timerOnce</b>(<i>callback</i>[, <i>delay</i>[, <i>time</i>]])
 
 Like [timer](#timer), except the timer automatically [stops](#timer_stop) on its first callback.
diff --git a/package.json b/package.json
index d4f4a62..0e4fc94 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "d3-timer",
-  "version": "0.1.2",
+  "version": "0.2.0",
   "description": "An efficient queue capable of managing thousands of concurrent animations.",
   "keywords": [
     "d3",
@@ -27,7 +27,7 @@
     "pretest": "mkdir -p build && node -e 'process.stdout.write(\"var version = \\\"\" + require(\"./package.json\").version + \"\\\"; export * from \\\"../index\\\"; export {version};\");' > build/bundle.js && rollup -f umd -n d3_timer -o build/d3-timer.js -- build/bundle.js",
     "test": "faucet `find test -name '*-test.js'` && eslint index.js src",
     "prepublish": "npm run test && uglifyjs build/d3-timer.js -c -m -o build/d3-timer.min.js && rm -f build/d3-timer.zip && zip -j build/d3-timer.zip -- LICENSE README.md build/d3-timer.js build/d3-timer.min.js",
-    "postpublish": "VERSION=`node -e 'console.log(require(\"./package.json\").version)'`; git push && git tag -am \"Release $VERSION.\" v${VERSION} && git push --tags && cp build/d3-timer.js ../d3.github.com/d3-timer.v0.1.js && cp build/d3-timer.min.js ../d3.github.com/d3-timer.v0.1.min.js && cd ../d3.github.com && git add d3-timer.v0.1.js d3-timer.v0.1.min.js && git commit -m \"d3-timer ${VERSION}\" && git push"
+    "postpublish": "VERSION=`node -e 'console.log(require(\"./package.json\").version)'`; git push && git tag -am \"Release $VERSION.\" v${VERSION} && git push --tags && cp build/d3-timer.js ../d3.github.com/d3-timer.v0.2.js && cp build/d3-timer.min.js ../d3.github.com/d3-timer.v0.2.min.js && cd ../d3.github.com && git add d3-timer.v0.2.js d3-timer.v0.2.min.js && git commit -m \"d3-timer ${VERSION}\" && git push"
   },
   "devDependencies": {
     "faucet": "0.0",
diff --git a/src/timer.js b/src/timer.js
index d107efc..362be57 100644
--- a/src/timer.js
+++ b/src/timer.js
@@ -1,9 +1,7 @@
 var frame = 0, // is an animation frame pending?
     timeout = 0, // is a timeout pending?
     taskHead,
-    taskTail,
-    taskId = 0,
-    taskById = {};
+    taskTail;
 
 var setFrame = typeof window !== "undefined"
     && (window.requestAnimationFrame
@@ -14,28 +12,28 @@ var setFrame = typeof window !== "undefined"
       || function(callback) { return setTimeout(callback, 17); };
 
 function Timer() {
-  this.id = ++taskId;
+  this._call =
+  this._time =
+  this._next = null;
 }
 
 Timer.prototype = timer.prototype = {
   restart: function(callback, delay, time) {
     if (typeof callback !== "function") throw new TypeError("callback is not a function");
     time = (time == null ? Date.now() : +time) + (delay == null ? 0 : +delay);
-    var i = this.id, t = taskById[i];
-    if (t) {
-      t.callback = callback, t.time = time;
-    } else {
-      t = {next: null, callback: callback, time: time};
-      if (taskTail) taskTail.next = t; else taskHead = t;
-      taskById[i] = taskTail = t;
+    if (!this._call) {
+      if (taskTail) taskTail._next = this;
+      else taskHead = this;
+      taskTail = this;
     }
+    this._call = callback;
+    this._time = time;
     sleep();
   },
   stop: function() {
-    var i = this.id, t = taskById[i];
-    if (t) {
-      t.callback = null, t.time = Infinity;
-      delete taskById[i];
+    if (this._call) {
+      this._call = null;
+      this._time = Infinity;
       sleep();
     }
   }
@@ -56,15 +54,26 @@ export function timerOnce(callback, delay, time) {
 export function timerFlush(now) {
   now = now == null ? Date.now() : +now;
   ++frame; // Pretend we’ve set an alarm, if we haven’t already.
-  try {
-    var t = taskHead, c;
-    while (t) {
-      if (now >= t.time) c = t.callback, c(now - t.time, now);
-      t = t.next;
+  var t = taskHead;
+  while (t) {
+    if (now >= t._time) t._call.call(null, now - t._time, now);
+    t = t._next;
+  }
+  --frame;
+}
+
+function timerSweep() {
+  var t0, t1 = taskHead, time = Infinity;
+  while (t1) {
+    if (t1._call) {
+      if (time > t1._time) time = t1._time;
+      t1 = (t0 = t1)._next;
+    } else {
+      t1 = t0 ? t0._next = t1._next : taskHead = t1._next;
     }
-  } finally {
-    --frame;
   }
+  taskTail = t0;
+  return time;
 }
 
 function wake() {
@@ -72,17 +81,8 @@ function wake() {
   try {
     timerFlush();
   } finally {
-    var t0, t1 = taskHead, time = Infinity;
-    while (t1) {
-      if (t1.callback) {
-        if (time > t1.time) time = t1.time;
-        t1 = (t0 = t1).next;
-      } else {
-        t1 = t0 ? t0.next = t1.next : taskHead = t1.next;
-      }
-    }
-    taskTail = t0;
-    sleep(time);
+    frame = 0;
+    sleep(timerSweep());
   }
 }
 
diff --git a/test/timer-test.js b/test/timer-test.js
index d5d6c9c..8876bd5 100644
--- a/test/timer-test.js
+++ b/test/timer-test.js
@@ -387,11 +387,3 @@ tape("timer.restart(callback, delay, time) recomputes the new wake time after on
     }, 100);
   }, 100);
 });
-
-tape("timer.id is a positive integer", function(test) {
-  var t = timer.timer(function() {});
-  test.ok(t.id > 0);
-  test.equal(t.id % 1, 0);
-  t.stop();
-  end(test);
-});