Add _.method as peer to _.property for capturing return values of fun…

…ctions on an Object. Closes jashkenas#2286: Underscore could use a _.propertyResult.

test/utility.js

@@ -95,6 +95,18 @@
     assert.equal(undefPropertyOf('curly'), void 0, 'should return undefined when obj is undefined');
   });
 
+  QUnit.test('method', function(assert) {
+    var stooge = {name: function() { return 'moe'; }, sum: function(a, b, c) { return a + b + c; }};
+    assert.equal(_.method('name')(stooge), 'moe', 'should return the results of calling the method with the given name');
+    assert.equal(_.method('sum')(stooge, 1, 2, 3), 6, 'should pass rest of arguments to named method for evaluation');
+    assert.equal(_.method(function() { return this.name(); })(stooge), 'moe', 'should apply a function literal passed.');
+    assert.equal(_.method(function(a, b, c) { return this.sum(a, b, c); })(stooge, 1, 2, 3), 6, 'should pass arguments when applying a function literal.');
+    assert.equal(_.method('macerena')(stooge), void 0, 'should return undefined for non-existant method name on defined object');
+    assert.equal(_.method('name')(null), void 0, 'should return undefined for null object');
+    assert.equal(_.method()(stooge), void 0, 'should return undefined for undefined method name on existing object');
+    assert.equal(_.method()(void 0), void 0, 'should return undefined for undefined method name on undefined object');
+  });
+
   QUnit.test('random', function(assert) {
     var array = _.range(1000);
     var min = Math.pow(2, 31);

underscore.js

@@ -1370,6 +1370,21 @@
 
   _.property = property;
 
+  // Generates a function for a given object that returns the passed function's return value.
+  // Accepts a method name or function literal for value.
+  // If value is a string, function assumes this string is a method name on the
+  // referenced object.
+  _.method = function(value) {
+    return restArgs(function(obj, args) {
+      if (obj == null) { return; }
+      var func = _.isFunction(value) ? value : obj[value];
+      if (func) {
+        return func.apply(obj, args);
+      }
+    });
+  };
+
+
   // Generates a function for a given object that returns a given property.
   _.propertyOf = function(obj) {
     return obj == null ? function(){} : function(key) {