Revert "Fixes #170, #266 ... throttle now starts at the beginning of the call."

This reverts commit bceb77e325.

test/functions.js

@@ -90,7 +90,7 @@ $(document).ready(function() {
     _.delay(function(){ ok(deferred, "deferred the function"); start(); }, 50);
   });
 
-  asyncTest("functions: throttle", 2, function() {
+  asyncTest("functions: throttle", 1, function() {
     var counter = 0;
     var incr = function(){ counter++; };
     var throttledIncr = _.throttle(incr, 100);
@@ -99,7 +99,6 @@ $(document).ready(function() {
     setTimeout(throttledIncr, 140);
     setTimeout(throttledIncr, 220);
     setTimeout(throttledIncr, 240);
-    _.delay(function(){ ok(counter == 1, "incr throttle was called immediately"); }, 40);
     _.delay(function(){ ok(counter == 3, "incr was throttled"); start(); }, 400);
   });
 

underscore.js

@@ -520,23 +520,8 @@
     return _.delay.apply(_, [func, 1].concat(slice.call(arguments, 1)));
   };
 
-  // Returns a function, that, when invoked, will only be triggered at most once
-  // during a given window of time.
-  _.throttle = function(func, wait) {
-    var ran = false;
-    return function() {
-      if (!ran) {
-        ran = true;
-        setTimeout(function(){ ran = false; }, wait);
-        return func.apply(this, arguments);
-      }
-    };
-  };
-
-  // Returns a function, that, as long as it continues to be invoked, will not
-  // be triggered. The function will be called after it stops being called for
-  // N milliseconds.
-  _.debounce = function(func, wait) {
+  // Internal function used to implement `_.throttle` and `_.debounce`.
+  var limit = function(func, wait, debounce) {
     var timeout;
     return function() {
       var context = this, args = arguments;
@@ -544,11 +529,24 @@
         timeout = null;
         func.apply(context, args);
       };
-      if (timeout) clearTimeout(timeout);
-      timeout = setTimeout(throttler, wait);
+      if (debounce) clearTimeout(timeout);
+      if (debounce || !timeout) timeout = setTimeout(throttler, wait);
     };
   };
 
+  // Returns a function, that, when invoked, will only be triggered at most once
+  // during a given window of time.
+  _.throttle = function(func, wait) {
+    return limit(func, wait, false);
+  };
+
+  // Returns a function, that, as long as it continues to be invoked, will not
+  // be triggered. The function will be called after it stops being called for
+  // N milliseconds.
+  _.debounce = function(func, wait) {
+    return limit(func, wait, true);
+  };
+
   // Returns a function that will be executed at most one time, no matter how
   // often you call it. Useful for lazy initialization.
   _.once = function(func) {