setInterval doesn't comply with DOM-version

[loyd]

Checked on x86_64, v0.10.30 and v0.11.14-pre, linux.

Firslty, setInterval determines delay between executions. For setInterval(sleep(20), 100):

------|====----------------|====----------------|====---
     0    20              120  140             240  260

DOM-version setInterval determines delay between runs:

------|====-----------|====-----------|====-----------|=
     0    20         100  120        200  220        300

Use the following snippet to check it out:

var prev = Date.now();
setInterval(function() {
  var s = Date.now();
  while(Date.now() - s < 20);
  var e = Date.now();
  console.log('Start', s, 'End', e, 'Delta', s - prev);
  prev = e;
}, 100);

Node v0.11.14-pre 'Delta': 102, 124, 119, 120, 120, ...
Node v0.10.30 'Delta': 101, 102, 100, 100, 100, ...
DOM 'Delta': 100, 80, 81, 80, 80, 81, ...

Secondly, overlay of calls:

var prev = Date.now();
setInterval(function() {
  var s = Date.now();
  while(Date.now() - s < 200);
  var e = Date.now();
  console.log('Start', s, 'End', e, 'Delta', s - prev);
  prev = e;
}, 100);

Node v0.11.14-pre 'Delta': 101, 302, 300, 300, 300, ...
Node v0.10.30 'Delta': 101, 101, 100, 100, ...
DOM 'Delta': 101, 0, 0, 1, 0, 1, 0, 0, ...

[loyd]

Well, the obvious solution of first is:

diff --git a/lib/timers.js b/lib/timers.js
index 3039b49..21d4003 100644
--- a/lib/timers.js
+++ b/lib/timers.js
@@ -284,8 +284,6 @@ exports.setInterval = function(callback, repeat) {
   return timer;

   function wrapper() {
-    callback.apply(this, args);
-    // If callback called clearInterval().
     if (timer._repeat === false) return;
     // If timer is unref'd (or was - it's permanently removed from the list.)
     if (this._handle) {
@@ -294,6 +292,8 @@ exports.setInterval = function(callback, repeat) {
       timer._idleTimeout = repeat;
       exports.active(timer);
     }
+
+    callback.apply(this, args);
   }
 };

[loyd]

Why should we implement interval over "idle timeout" pattern as timeouts?