Initial draft of _.throttle and _.debounce

jashkenas · jashkenas · commit 9e3e067f5025 · 2010-11-30T11:41:48.000-05:00
diff --git a/test/functions.js b/test/functions.js
@@ -54,19 +54,44 @@ $(document).ready(function() {
     equals(fastFib(10), 55, 'a memoized version of fibonacci produces identical results');
   });
 
-  asyncTest("functions: delay", function() {
+  asyncTest("functions: delay", 2, function() {
     var delayed = false;
     _.delay(function(){ delayed = true; }, 100);
     _.delay(function(){ ok(!delayed, "didn't delay the function quite yet"); }, 50);
     _.delay(function(){ ok(delayed, 'delayed the function'); start(); }, 150);
   });
 
-  asyncTest("functions: defer", function() {
+  asyncTest("functions: defer", 1, function() {
     var deferred = false;
     _.defer(function(bool){ deferred = bool; }, true);
     _.delay(function(){ ok(deferred, "deferred the function"); start(); }, 50);
   });
 
+  asyncTest("functions: throttle", 1, function() {
+    var counter = 0;
+    var incr = function(){ counter++; };
+    var throttledIncr = _.throttle(incr, 50);
+    throttledIncr(); throttledIncr(); throttledIncr();
+    setTimeout(throttledIncr, 60);
+    setTimeout(throttledIncr, 70);
+    setTimeout(throttledIncr, 110);
+    setTimeout(throttledIncr, 120);
+    _.delay(function(){ ok(counter == 3, "incr was throttled"); start(); }, 180);
+  });
+
+  asyncTest("functions: debounce", 1, function() {
+    var counter = 0;
+    var incr = function(){ counter++; };
+    var debouncedIncr = _.debounce(incr, 50);
+    debouncedIncr(); debouncedIncr(); debouncedIncr();
+    setTimeout(debouncedIncr, 30);
+    setTimeout(debouncedIncr, 60);
+    setTimeout(debouncedIncr, 90);
+    setTimeout(debouncedIncr, 120);
+    setTimeout(debouncedIncr, 150);
+    _.delay(function(){ ok(counter == 1, "incr was debounced"); start(); }, 220);
+  });
+
   test("functions: wrap", function() {
     var greet = function(name){ return "hi: " + name; };
     var backwards = _.wrap(greet, function(func, name){ return func(name) + ' ' + name.split('').reverse().join(''); });
diff --git a/test/objects.js b/test/objects.js
@@ -11,15 +11,6 @@ $(document).ready(function() {
   });
 
   test("objects: functions", function() {
-    var expected = ["all", "any", "bind", "bindAll", "breakLoop", "clone", "compact",
-    "compose", "contains", "defer", "delay", "detect", "each", "every", "extend", "filter", "find", "first",
-    "flatten", "foldl", "foldr", "forEach", "functions", "head", "identity", "include",
-    "indexOf", "inject", "intersect", "invoke", "isArguments", "isArray", "isBoolean", "isDate", "isElement", "isEmpty", "isEqual",
-    "isFunction", "isNaN", "isNull", "isNumber", "isRegExp", "isString", "isUndefined", "keys", "last", "lastIndexOf", "map", "max",
-    "memoize", "methods", "min", "mixin", "noConflict", "pluck", "range", "reduce", "reduceRight", "reject", "rest", "select",
-    "size", "some", "sortBy", "sortedIndex", "tail", "tap", "template", "times", "toArray", "uniq", "unique",
-    "uniqueId", "values", "without", "wrap", "zip"];
-    same(expected, _.methods(_), 'provides a sorted list of functions');
     var obj = {a : 'dash', b : _.map, c : (/yo/), d : _.reduce};
     ok(_.isEqual(['b', 'd'], _.functions(obj)), 'can grab the function names of any passed-in object');
   });
diff --git a/underscore.js b/underscore.js
@@ -419,6 +419,33 @@
     return _.delay.apply(_, [func, 1].concat(slice.call(arguments, 1)));
   };
 
+  // Internal function used to implement `_.throttle` and `_.debounce`.
+  var limit = function(func, wait, debounce) {
+    var timeout;
+    return function() {
+      var context = this, args = arguments;
+      var throttler = function() {
+        timeout = null;
+        func.apply(context, args);
+      };
+      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 the first function passed as an argument to the second,
   // allowing you to adjust arguments, run code before and after, and
   // conditionally execute the original function.
