implement HashMap.update

src/HashMap/docs.md

@@ -31,6 +31,12 @@ Adds all values from the data to the hashMap. Each key:value pair in the object
 
 Removes the key and value from the hashMap.
 
+### `update(key, updateFn)`
+
+Updates the key with the return value of `updateFn(state[key])`.
+
+`updateFn` recieves the current value at `key` or null if undefined.
+
 ## Example
 
 ```js

src/HashMap/index.js

@@ -24,6 +24,12 @@ export default function HashMap (name, initialState = {}){
                 type: createActionType('delete'),
                 key
             })
+        },
+        update(key, updateFn){
+            return ({
+                type: createActionType('update'),
+                key, updateFn
+            })
         }
     }
 
@@ -47,6 +53,12 @@ export default function HashMap (name, initialState = {}){
                     ? { ...nextState, [key]: state[key] }
                     : nextState
             , {})
+        } else if(action.type.endsWith('update')){
+            const { key, updateFn } = action
+            return {
+                ...state,
+                [key]: updateFn(state[key] || null)
+            }
         } else return state
     }
 

src/HashMap/test/hashmap.test.js

@@ -50,7 +50,20 @@ test('HashMap', main => {
         const state0 = reducer({ 1: 'a', 2: 'b' }, actions.delete(1))
         t.deepEqual(state0, { 2: 'b' }, 'should have deleted the element at key')
         const state1 = reducer(state0, actions.delete(1))
-        t.deepEqual(state0, { 2: 'b' }, 'should have done nothing when the key does not exist')
+        t.deepEqual(state1, { 2: 'b' }, 'should have done nothing when the key does not exist')
+        t.end()
+    })
+    main.test('`update` action', t => {
+        const { actions, reducer } = HashMap('test-name-5')
+        const state0 = reducer({ 1: 'a', 2: 'b' }, actions.update(1, value => {
+            t.equal(value, 'a', 'should be given the current value')
+            return 'z'
+        }))
+        t.deepEqual(state0, { 1: 'z', 2: 'b' }, 'should have updated the element at key with the return value')
+        const state1 = reducer(state0, actions.update(3, value => {
+            t.equal(value, null, 'value should be null when it does not exist')
+        }))
+        t.deepEqual(state1, {...state0, 3: undefined}, 'should have set to undefined')
         t.end()
     })
     main.test('multiple instances', t => {