$apply command for update

Author: brandonbloom

src/addons/__tests__/update-test.js

@@ -78,6 +78,14 @@ describe('update', function() {
     expect(update({a: 'b'}, {$set: {c: 'd'}})).toEqual({c: 'd'});
   });
 
+  it('should support apply', function() {
+    expect(update(2, {$apply: function(x) { return x * 2; }})).toEqual(4);
+    expect(update.bind(null, 2, {$apply: 123})).toThrow(
+      'Invariant Violation: update(): expected spec of $apply to be a ' +
+      'function; got 123.'
+    );
+  });
+
   it('should support deep updates', function() {
     expect(update({a: 'b', c: {d: 'e'}}, {c: {d: {$set: 'f'}}})).toEqual({
       a: 'b',
@@ -88,8 +96,8 @@ describe('update', function() {
   it('should require a command', function() {
     expect(update.bind(null, {a: 'b'}, {a: 'c'})).toThrow(
       'Invariant Violation: update(): You provided a key path to update() ' +
-      'that did not contain one of $push, $unshift, $splice, $set, $merge. ' +
-      'Did you forget to include {$set: ...}?'
+      'that did not contain one of $push, $unshift, $splice, $set, $merge, ' +
+      '$apply. Did you forget to include {$set: ...}?'
     );
   });
 });

src/addons/update.js

@@ -37,13 +37,15 @@ var COMMAND_UNSHIFT = keyOf({$unshift: null});
 var COMMAND_SPLICE = keyOf({$splice: null});
 var COMMAND_SET = keyOf({$set: null});
 var COMMAND_MERGE = keyOf({$merge: null});
+var COMMAND_APPLY = keyOf({$apply: null});
 
 var ALL_COMMANDS_LIST = [
   COMMAND_PUSH,
   COMMAND_UNSHIFT,
   COMMAND_SPLICE,
   COMMAND_SET,
-  COMMAND_MERGE
+  COMMAND_MERGE,
+  COMMAND_APPLY
 ];
 
 var ALL_COMMANDS_SET = {};
@@ -147,6 +149,16 @@ function update(value, spec) {
     });
   }
 
+  if (spec.hasOwnProperty(COMMAND_APPLY)) {
+    invariant(
+      typeof spec[COMMAND_APPLY] === 'function',
+      'update(): expected spec of %s to be a function; got %s.',
+      COMMAND_APPLY,
+      spec[COMMAND_APPLY]
+    );
+    nextValue = spec[COMMAND_APPLY](nextValue);
+  }
+
   for (var k in spec) {
     if (!(ALL_COMMANDS_SET.hasOwnProperty(k) && ALL_COMMANDS_SET[k])) {
       nextValue[k] = update(value[k], spec[k]);