add $delete command to addons.update

docs/docs/09.6-update.md

@@ -62,6 +62,7 @@ The `$`-prefixed keys are called *commands*. The data structure they are "mutati
   * `{$set: any}` replace the target entirely.
   * `{$merge: object}` merge the keys of `object` with the target.
   * `{$apply: function}` passes in the current value to the function and updates it with the new returned value.
+  * `{$unset: string} deletes the given key or array/object of keys from the target. If target is an array, values are set to `null`.
 
 ## Examples
 

src/addons/__tests__/update-test.js

@@ -79,6 +79,17 @@ describe('update', function() {
     );
   });
 
+  it('should support unset', function() {
+    expect(update({a:1,b:2}, {$unset:'b'})).toEqual({a:1});
+    expect(update({a:1,b:2,c:3}, {$unset:['a','c','d']})).toEqual({b:2});
+    expect(update({a:1,b:2,c:3}, {$unset:{'a':'','b':''}})).toEqual({c:3});
+    expect(update(['a','b','c'], {$unset:[1,'foo',5]})).toEqual(['a',null,'c']);
+    expect(update.bind(null, 2, {$unset: 'foo'})).toThrow(
+      'Invariant Violation: update(): expected target of $unset to be an ' +
+      'object or array; got 2.'
+    );
+  });
+
   it('should support deep updates', function() {
     expect(update({a: 'b', c: {d: 'e'}}, {c: {d: {$set: 'f'}}})).toEqual({
       a: 'b',
@@ -90,7 +101,7 @@ describe('update', 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, $merge, ' +
-      '$apply. Did you forget to include {$set: ...}?'
+      '$apply, $unset. Did you forget to include {$set: ...}?'
     );
   });
 });

src/addons/update.js

@@ -30,14 +30,16 @@ 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 COMMAND_DELETE = keyOf({$unset: null});
 
 var ALL_COMMANDS_LIST = [
   COMMAND_PUSH,
   COMMAND_UNSHIFT,
   COMMAND_SPLICE,
   COMMAND_SET,
   COMMAND_MERGE,
-  COMMAND_APPLY
+  COMMAND_APPLY,
+  COMMAND_DELETE
 ];
 
 var ALL_COMMANDS_SET = {};
@@ -151,6 +153,34 @@ function update(value, spec) {
     nextValue = spec[COMMAND_APPLY](nextValue);
   }
 
+  if (spec.hasOwnProperty(COMMAND_DELETE)) {
+    var arg = spec[COMMAND_DELETE], delKeys;
+    if (Array.isArray(arg)){
+      delKeys = arg;
+    } else if (typeof arg === 'object') {
+      delKeys = Object.keys(arg);
+    } else {
+      delKeys = [arg];
+    }
+    invariant(
+      nextValue && (Array.isArray(nextValue) || typeof nextValue === 'object'),
+      'update(): expected target of %s to be an object or array; got %s.',
+      COMMAND_DELETE,
+      nextValue
+    );
+    if (Array.isArray(nextValue)){
+      delKeys.forEach(function(i){
+        if (nextValue.propertyIsEnumerable(i)) {
+          nextValue[i] = null;
+        }
+      });
+    } else {
+      delKeys.forEach(function(delKey){
+        delete nextValue[delKey];
+      });
+    }
+  }
+
   for (var k in spec) {
     if (!(ALL_COMMANDS_SET.hasOwnProperty(k) && ALL_COMMANDS_SET[k])) {
       nextValue[k] = update(value[k], spec[k]);