optimize Util.throttle to create fewer timeouts

scripts/tests/throttle-test.js

@@ -0,0 +1,34 @@
+var Util = require("../../lib/common-util");
+
+(function (throttle) {
+    var last = 0;
+    var last_call = 0;
+    var f = Util.throttle(function (boop) {
+        var now = +new Date();
+        if (last) {
+            console.log("last execution was %sms ago", now - last);
+        } else {
+            console.log("this is the first execution");
+        }
+        last = now;
+
+        //console.log('time of execution:', now);
+        console.log(boop);
+    }, 1000);
+
+    [150, 250, 580, 850, 1500, 2200, 3990, 5000].forEach(function (delay) {
+        setTimeout(function () {
+            var now = +new Date();
+
+            if (last_call) {
+                console.log("last call was %sms ago", now - last_call);
+            }
+
+            last_call = now;
+            //console.log("time of call for delay(%s):", delay, now);
+            f(delay);
+        }, delay);
+    });
+}(Util.throttle2));
+
+

www/common/common-util.js

@@ -306,11 +306,43 @@
     };
 
     Util.throttle = function (f, ms) {
+        var last = 0;
         var to;
+        var args;
+
+        var defer = function (delay) {
+            // no timeout: run function `f` in `ms` milliseconds
+            // unless `g` is called again in the meantime
+            to = setTimeout(function () {
+                // wipe the current timeout handler
+                to = undefined;
+
+                // take the current time
+                var now = +new Date();
+                // compute time passed since `last`
+                var diff = now - last;
+                if (diff < ms) {
+                    // don't run `f` if `g` was called since this timeout was set
+                    // instead calculate how much further in the future your next
+                    // timeout should be scheduled
+                    return void defer(ms - diff);
+                }
+
+                // else run `f` with the most recently supplied arguments
+                f.apply(null, args);
+            }, delay);
+        };
+
         var g = function () {
-            clearTimeout(to);
-            to = setTimeout(Util.bake(f, Util.slice(arguments)), ms);
+            // every time you call this function store the time
+            last = +new Date();
+            // remember what arguments were passed
+            args = Util.slice(arguments);
+            // if there is a pending timeout then do nothing
+            if (to) { return; }
+            defer(ms);
         };
+
         g.clear = function () {
             clearTimeout(to);
             to = undefined;