Reduce recalculation needed for RelativeDates

Capture more state in closure scopes. Pretty clever, at the expense of
simplicity.

4chan_x.user.js

@@ -3558,11 +3558,11 @@
     node: function(post) {
       var dateEl, diff, utc;
       dateEl = $('.postInfo > .dateTime', post.el);
-      utc = dateEl.dataset.utc * 1000;
       dateEl.title = dateEl.textContent;
+      utc = dateEl.dataset.utc * 1000;
       diff = Date.now() - utc;
       dateEl.textContent = RelativeDates.relative(diff);
-      RelativeDates.setUpdate(dateEl, diff);
+      RelativeDates.setUpdate(dateEl, utc, diff);
       return RelativeDates.flush();
     },
     relative: function(diff) {
@@ -3576,29 +3576,38 @@
     },
     stale: [],
     flush: $.debounce($.SECOND, function() {
-      var dateEl, diff, _i, _len, _ref;
+      var now, update, _i, _len, _ref;
       if (d.hidden) {
         return;
       }
+      now = Date.now();
       _ref = RelativeDates.stale;
       for (_i = 0, _len = _ref.length; _i < _len; _i++) {
-        dateEl = _ref[_i];
-        if (d.contains(dateEl)) {
-          diff = Date.now() - dateEl.dataset.utc * 1000;
-          dateEl.textContent = RelativeDates.relative(diff);
-          RelativeDates.setUpdate(dateEl, diff);
-        }
+        update = _ref[_i];
+        update(now);
       }
       RelativeDates.stale = [];
       clearTimeout(RelativeDates.timeout);
       return RelativeDates.timeout = setTimeout(RelativeDates.flush, RelativeDates.INTERVAL);
     }),
-    setUpdate: function(dateEl, diff) {
-      var delay;
-      delay = diff > $.HOUR ? diff % $.HOUR : diff > $.MINUTE ? diff % $.MINUTE : diff % $.SECOND;
-      return setTimeout((function() {
-        return RelativeDates.stale.push(dateEl);
-      }), delay);
+    setUpdate: function(dateEl, utc, diff) {
+      var markStale, setOwnTimeout, update;
+      setOwnTimeout = function(diff) {
+        var delay;
+        delay = diff > $.HOUR ? diff % $.HOUR : diff > $.MINUTE ? diff % $.MINUTE : diff % $.SECOND;
+        return setTimeout(markStale, delay);
+      };
+      update = function(now) {
+        if (d.contains(dateEl)) {
+          diff = now - utc;
+          dateEl.textContent = RelativeDates.relative(diff);
+          return setOwnTimeout(diff);
+        }
+      };
+      markStale = function() {
+        return RelativeDates.stale.push(update);
+      };
+      return setOwnTimeout(diff);
     }
   };
 

script.coffee

@@ -2849,17 +2849,18 @@ RelativeDates =
   node: (post) ->
     dateEl = $ '.postInfo > .dateTime', post.el
 
-    utc = dateEl.dataset.utc * 1000 # convert data-utc to milliseconds
-
     # Show original absolute time as tooltip so users can still know exact times
     # Since "Time Formatting" runs `node` before us, the title tooltip will
     # pick up the user-formatted time instead of 4chan time when enabled.
     dateEl.title = dateEl.textContent
 
+    # convert data-utc to milliseconds
+    utc = dateEl.dataset.utc * 1000
+
     diff = Date.now() - utc
 
     dateEl.textContent = RelativeDates.relative diff
-    RelativeDates.setUpdate dateEl, diff
+    RelativeDates.setUpdate dateEl, utc, diff
 
     # Main calls @node whenever a DOM node is added (update, inline post,
     # whatever), so use also this reflow opportunity to flush any other dates
@@ -2889,31 +2890,44 @@ RelativeDates =
   # stuttering won't be noticed), falling back to INTERVAL while the page
   # is visible.
   #
-  # each individual dateTime element will be added to the stale list when it
-  # needs to change.
+  # each individual dateTime element will add its update() function to the stale list
+  # when it to be called.
   stale: []
   flush: $.debounce($.SECOND, ->
     # no point in changing the dates until the user sees them
     return if d.hidden
-    for dateEl in RelativeDates.stale
-      if d.contains dateEl # not removed from DOM
-        diff = Date.now() - dateEl.dataset.utc * 1000
-        dateEl.textContent = RelativeDates.relative diff
-        RelativeDates.setUpdate dateEl, diff
+
+    now = Date.now()
+    update now for update in RelativeDates.stale
     RelativeDates.stale = []
+
+    # reset automatic flush
     clearTimeout RelativeDates.timeout
     RelativeDates.timeout = setTimeout RelativeDates.flush, RelativeDates.INTERVAL)
 
-  # Add element to stale list when the relative date string would change
-  # diff is in milliseconds between dateEl and now
-  setUpdate: (dateEl, diff) ->
-    delay = if diff > $.HOUR
-      diff % $.HOUR
-    else if diff > $.MINUTE
-      diff % $.MINUTE
-    else
-      diff % $.SECOND
-    setTimeout (-> RelativeDates.stale.push dateEl), delay
+  # create function `update()`, closed over dateEl and diff, that, when called
+  # from `flush()`, updates the element, and re-calls `setOwnTimeout()` to
+  # re-add `update()` to the stale list later.
+  setUpdate: (dateEl, utc, diff) ->
+    setOwnTimeout = (diff) ->
+      delay = if diff > $.HOUR
+        diff % $.HOUR
+      else if diff > $.MINUTE
+        diff % $.MINUTE
+      else
+        diff % $.SECOND
+      setTimeout markStale, delay
+
+    update = (now) ->
+      if d.contains dateEl # not removed from DOM
+        diff = now - utc
+        dateEl.textContent = RelativeDates.relative diff
+        setOwnTimeout diff
+
+    markStale = -> RelativeDates.stale.push update
+
+    # kick off initial timeout with current diff
+    setOwnTimeout diff
 
 FileInfo =
   init: ->