Add test for timer.

Also fix a minor bug where we might miss the delay the first callback by an
extra frame, and allow d3.timer to be called with an optional delay.

d3.js

@@ -1963,7 +1963,7 @@ function d3_transition(groups) {
         delay[++k] = delayMin;
       });
     }
-    d3_timer(step, delayMin);
+    d3.timer(step, delayMin);
     return transition;
   };
 
@@ -2083,17 +2083,14 @@ var d3_timer_queue = null,
     d3_timer_timeout; // is a timeout active?
 
 // The timer will continue to fire until callback returns true.
-d3.timer = function(callback) {
-  d3_timer(callback, 0);
-};
-
-function d3_timer(callback, delay) {
+d3.timer = function(callback, delay) {
   var now = Date.now(),
       found = false,
       t0,
       t1 = d3_timer_queue;
 
-  if (!isFinite(delay)) return;
+  if (arguments.length < 2) delay = 0;
+  else if (!isFinite(delay)) return;
 
   // See if the callback's already in the queue.
   while (t1) {
@@ -2130,7 +2127,7 @@ function d3_timer_step() {
 
   while (t1) {
     elapsed = now - t1.then;
-    if (elapsed > t1.delay) t1.flush = t1.callback(elapsed);
+    if (elapsed >= t1.delay) t1.flush = t1.callback(elapsed);
     t1 = t1.next;
   }
 

src/core/timer.js

@@ -3,17 +3,14 @@ var d3_timer_queue = null,
     d3_timer_timeout; // is a timeout active?
 
 // The timer will continue to fire until callback returns true.
-d3.timer = function(callback) {
-  d3_timer(callback, 0);
-};
-
-function d3_timer(callback, delay) {
+d3.timer = function(callback, delay) {
   var now = Date.now(),
       found = false,
       t0,
       t1 = d3_timer_queue;
 
-  if (!isFinite(delay)) return;
+  if (arguments.length < 2) delay = 0;
+  else if (!isFinite(delay)) return;
 
   // See if the callback's already in the queue.
   while (t1) {
@@ -50,7 +47,7 @@ function d3_timer_step() {
 
   while (t1) {
     elapsed = now - t1.then;
-    if (elapsed > t1.delay) t1.flush = t1.callback(elapsed);
+    if (elapsed >= t1.delay) t1.flush = t1.callback(elapsed);
     t1 = t1.next;
   }
 

src/core/transition.js

@@ -123,7 +123,7 @@ function d3_transition(groups) {
         delay[++k] = delayMin;
       });
     }
-    d3_timer(step, delayMin);
+    d3.timer(step, delayMin);
     return transition;
   };
 

test/core/timer-test.js

@@ -0,0 +1,62 @@
+require("../env");
+require("../../d3");
+
+var vows = require("vows"),
+    assert = require("assert");
+
+var suite = vows.describe("d3.timer");
+
+suite.addBatch({
+  "timer": {
+    topic: function() {
+      return d3.timer;
+    },
+    "with no delay": {
+      topic: timer(),
+      "first calls after 17 ms or less": function(info) {
+        assert.inDelta(info.start - info.scheduled, 17, 15);
+      },
+      "calls until the function returns true": function(info) {
+        assert.equal(info.count, 4);
+      },
+      "calls every 17 ms": function(info) {
+        assert.inDelta(info.stop - info.start, 17 * 3, 15);
+      }
+    },
+    "with a specified delay": {
+      topic: timer(250),
+      "first calls after the delay": function(info) {
+        assert.inDelta(info.start - info.scheduled, 250, 15);
+      },
+      "calls until the function returns true": function(info) {
+        assert.equal(info.count, 4);
+      },
+      "calls every 17 ms": function(info) {
+        assert.inDelta(info.stop - info.start, 17 * 3, 15);
+      }
+    }
+  }
+});
+
+function timer(delay) {
+  var args = Array.prototype.slice.call(arguments);
+  return function() {
+    var cb = this.callback,
+        info = {scheduled: Date.now(), count: 0};
+
+    args.unshift(function() {
+      var count = ++info.count;
+      if (count === 1) {
+        info.start = Date.now();
+      } else if (count === 4) {
+        info.stop = Date.now();
+        cb(null, info);
+        return true;
+      }
+    });
+
+    d3.timer.apply(this, args);
+  };
+}
+
+suite.export(module);