correct for drift

1 files changed, 10 insertions, 4 deletions

diff --git a/tempo.js b/tempo.js
index 682cb75..7b471ae 100644
--- a/tempo.js
+++ b/tempo.js
@@ -29,6 +29,14 @@ function updateTime() {
 		dd + ' ' + MONTHS[dm] + ' ' + dy;
 }
 
+// recursively calling setTimeout instead of using setInterval allows us to
+// correct for any drift caused by imprecise delays.
+function updateTimeRecursive() {
+	updateTime();
+	// +1ms to avoid updating too early
+	setTimeout(updateTimeRecursive, 1001 - new Date().getTime() % 1000);
+}
+
 function startTempo() {
 	timefmt = localStorage['timefmt'];
 
@@ -40,11 +48,9 @@ function startTempo() {
 	if ((val = localStorage['bg']))
 		document.body.style.backgroundColor = val;
 
-	updateTime();
-	setTimeout(function() { updateTime(); setInterval(updateTime, 1000) },
-		1000 - (new Date()).getTime() % 1000);
+	updateTimeRecursive();
 }
 
 window.onload = startTempo;
 
-document.addEventListener('contextmenu', function(e) { e.preventDefault() });
+document.addEventListener('contextmenu', e => e.preventDefault());