Issue #70 -- implementing each, find, all, any, etc. without the use of a try/catch/throw. Minor speedup + avoids destroying the stack trace.

test/collections.js

@@ -7,10 +7,6 @@ $(document).ready(function() {
       equals(num, i + 1, 'each iterators provide value and iteration count');
     });
 
-    var answer = null;
-    _.each([1, 2, 3], function(num){ if ((answer = num) == 2) _.breakLoop(); });
-    equals(answer, 2, 'the loop broke in the middle');
-
     var answers = [];
     _.each([1, 2, 3], function(num){ answers.push(num * this.multiplier);}, {multiplier : 5});
     equals(answers.join(', '), '5, 10, 15', 'context object property accessed');
@@ -65,7 +61,7 @@ $(document).ready(function() {
 
     sum = _([1, 2, 3]).reduce(function(sum, num){ return sum + num; }, 0);
     equals(sum, 6, 'OO-style reduce');
-    
+
     var sum = _.reduce([1, 2, 3], function(sum, num){ return sum + num; });
     equals(sum, 6, 'default initial value');
   });
@@ -73,10 +69,10 @@ $(document).ready(function() {
   test('collections: reduceRight', function() {
     var list = _.reduceRight(["foo", "bar", "baz"], function(memo, str){ return memo + str; }, '');
     equals(list, 'bazbarfoo', 'can perform right folds');
-    
+
     var list = _.foldr(["foo", "bar", "baz"], function(memo, str){ return memo + str; }, '');
     equals(list, 'bazbarfoo', 'aliased as "foldr"');
-    
+
     var list = _.foldr(["foo", "bar", "baz"], function(memo, str){ return memo + str; });
     equals(list, 'bazbarfoo', 'default initial value');
   });

test/utility.js

@@ -15,15 +15,6 @@ $(document).ready(function() {
     equals(_.identity(moe), moe, 'moe is the same as his identity');
   });
 
-  test('utility: breakLoop', function() {
-    var result = null;
-    _([1,2,3,4,5,6]).each(function(num) {
-      result = num;
-      if (num == 3) _.breakLoop();
-    });
-    equals(result, 3, 'broke out of a loop');
-  });
-
   test("utility: uniqueId", function() {
     var ids = [], i = 0;
     while(i++ < 100) ids.push(_.uniqueId());

underscore.js

@@ -17,8 +17,8 @@
   // Save the previous value of the `_` variable.
   var previousUnderscore = root._;
 
-  // Establish the object that gets thrown to break out of a loop iteration.
-  var breaker = typeof StopIteration !== 'undefined' ? StopIteration : '__break__';
+  // Establish the object that gets returned to break out of a loop iteration.
+  var breaker = {};
 
   // Save bytes in the minified (but not gzipped) version:
   var ArrayProto = Array.prototype, ObjProto = Object.prototype;
@@ -67,20 +67,20 @@
   // Handles objects implementing `forEach`, arrays, and raw objects.
   // Delegates to **ECMAScript 5**'s native `forEach` if available.
   var each = _.each = _.forEach = function(obj, iterator, context) {
-    try {
-      if (nativeForEach && obj.forEach === nativeForEach) {
-        obj.forEach(iterator, context);
-      } else if (_.isNumber(obj.length)) {
-        for (var i = 0, l = obj.length; i < l; i++) iterator.call(context, obj[i], i, obj);
-      } else {
-        for (var key in obj) {
-          if (hasOwnProperty.call(obj, key)) iterator.call(context, obj[key], key, obj);
+    var value;
+    if (nativeForEach && obj.forEach === nativeForEach) {
+      obj.forEach(iterator, context);
+    } else if (_.isNumber(obj.length)) {
+      for (var i = 0, l = obj.length; i < l; i++) {
+        if (iterator.call(context, obj[i], i, obj) === breaker) return;
+      }
+    } else {
+      for (var key in obj) {
+        if (hasOwnProperty.call(obj, key)) {
+          if (iterator.call(context, obj[key], key, obj) === breaker) return;
         }
       }
-    } catch(e) {
-      if (e != breaker) throw e;
     }
-    return obj;
   };
 
   // Return the results of applying the iterator to each element.
@@ -126,10 +126,10 @@
   // Return the first value which passes a truth test. Aliased as `detect`.
   _.find = _.detect = function(obj, iterator, context) {
     var result;
-    each(obj, function(value, index, list) {
+    any(obj, function(value, index, list) {
       if (iterator.call(context, value, index, list)) {
         result = value;
-        _.breakLoop();
+        return true;
       }
     });
     return result;
@@ -164,7 +164,7 @@
     if (nativeEvery && obj.every === nativeEvery) return obj.every(iterator, context);
     var result = true;
     each(obj, function(value, index, list) {
-      if (!(result = result && iterator.call(context, value, index, list))) _.breakLoop();
+      if (!(result = result && iterator.call(context, value, index, list))) return breaker;
     });
     return result;
   };
@@ -172,12 +172,12 @@
   // Determine if at least one element in the object matches a truth test.
   // Delegates to **ECMAScript 5**'s native `some` if available.
   // Aliased as `any`.
-  _.some = _.any = function(obj, iterator, context) {
+  var any = _.some = _.any = function(obj, iterator, context) {
     iterator = iterator || _.identity;
     if (nativeSome && obj.some === nativeSome) return obj.some(iterator, context);
     var result = false;
     each(obj, function(value, index, list) {
-      if (result = iterator.call(context, value, index, list)) _.breakLoop();
+      if (result = iterator.call(context, value, index, list)) return breaker;
     });
     return result;
   };
@@ -187,8 +187,8 @@
   _.include = _.contains = function(obj, target) {
     if (nativeIndexOf && obj.indexOf === nativeIndexOf) return obj.indexOf(target) != -1;
     var found = false;
-    each(obj, function(value) {
-      if (found = value === target) _.breakLoop();
+    any(obj, function(value) {
+      if (found = value === target) return true;
     });
     return found;
   };
@@ -642,11 +642,6 @@
     for (var i = 0; i < n; i++) iterator.call(context, i);
   };
 
-  // Break out of the middle of an iteration.
-  _.breakLoop = function() {
-    throw breaker;
-  };
-
   // Add your own custom functions to the Underscore object, ensuring that
   // they're correctly added to the OOP wrapper as well.
   _.mixin = function(obj) {