Return a copy instead of mutating client presence state

CHANGELOG.md

@@ -11,6 +11,9 @@ See these [`1.1.x` to `1.2.x` upgrade instructions](https://gist.github.com/chri
 * JavaScript client enhancements
   * Use return value of channel onMessage callback for specialized message transformations before dispatching to the channel
 
+* JavaScript client backward incompatible changes
+  * `Presence.syncState` and `Presence.syncDiff` now return a copy of the state instead of mutating it
+
 ## 1.2.0-rc.1 (2016-05-25)
 
 See these [`1.1.x` to `1.2.x` upgrade instructions](https://gist.github.com/chrismccord/29100e16d3990469c47f851e3142f766) to bring your existing apps up to speed.

web/static/js/phoenix.js

@@ -127,7 +127,7 @@
 // they came online from:
 //
 //     let state = {}
-//     Presence.syncState(state, stateFromServer)
+//     state = Presence.syncState(state, stateFromServer)
 //     let listBy = (id, {metas: [first, ...rest]}) => {
 //       first.count = rest.length + 1 // count of this user's presences
 //       first.id = id
@@ -157,12 +157,12 @@
 //     let presences = {} // client's initial empty presence state
 //     // receive initial presence data from server, sent after join
 //     myChannel.on("presences", state => {
-//       Presence.syncState(presences, state, onJoin, onLeave)
+//       presences = Presence.syncState(presences, state, onJoin, onLeave)
 //       displayUsers(Presence.list(presences))
 //     })
 //     // receive "presence_diff" from server, containing join/leave events
 //     myChannel.on("presence_diff", diff => {
-//       Presence.syncDiff(presences, diff, onJoin, onLeave)
+//       presences = Presence.syncDiff(presences, diff, onJoin, onLeave)
 //       this.setState({users: Presence.list(room.presences, listBy)})
 //     })
 //
@@ -795,13 +795,14 @@ Ajax.states = {complete: 4}
 
 export var Presence = {
 
-  syncState(state, newState, onJoin, onLeave){
+  syncState(currentState, newState, onJoin, onLeave){
+    let state = this.clone(currentState)
     let joins = {}
     let leaves = {}
 
     this.map(state, (key, presence) => {
       if(!newState[key]){
-        leaves[key] = this.clone(presence)
+        leaves[key] = presence
       }
     })
     this.map(newState, (key, newPresence) => {
@@ -823,10 +824,11 @@ export var Presence = {
         joins[key] = newPresence
       }
     })
-    this.syncDiff(state, {joins: joins, leaves: leaves}, onJoin, onLeave)
+    return this.syncDiff(state, {joins: joins, leaves: leaves}, onJoin, onLeave)
   },
 
-  syncDiff(state, {joins, leaves}, onJoin, onLeave){
+  syncDiff(currentState, {joins, leaves}, onJoin, onLeave){
+    let state = this.clone(currentState)
     if(!onJoin){ onJoin = function(){} }
     if(!onLeave){ onLeave = function(){} }
 
@@ -850,6 +852,7 @@ export var Presence = {
         delete state[key]
       }
     })
+    return state
   },
 
   list(presences, chooser){

web/test/presence_test.js

@@ -2,6 +2,8 @@ import assert from "assert"
 
 import {Presence} from "../static/js/phoenix"
 
+let clone = (obj) => { return JSON.parse(JSON.stringify(obj)) }
+
 let fixtures = {
   joins(){
     return {u1: {metas: [{id: 1, phx_ref: "1.2"}]}}
@@ -22,7 +24,11 @@ describe("syncState", () => {
   it("syncs empty state", () => {
     let newState = {u1: {metas: [{id: 1, phx_ref: "1"}]}}
     let state = {}
+    let stateBefore = clone(state)
     Presence.syncState(state, newState)
+    assert.deepEqual(state, stateBefore)
+
+    state = Presence.syncState(state, newState)
     assert.deepEqual(state, newState)
   })
 
@@ -37,7 +43,11 @@ describe("syncState", () => {
     let onLeave = (key, current, leftPres) => {
       left[key] = {current: current, leftPres: leftPres}
     }
+    let stateBefore = clone(state)
     Presence.syncState(state, newState, onJoin, onLeave)
+    assert.deepEqual(state, stateBefore)
+
+    state = Presence.syncState(state, newState, onJoin, onLeave)
     assert.deepEqual(state, newState)
     assert.deepEqual(joined, {
       u1: {current: null, newPres: {metas: [{id: 1, phx_ref: "1"}]}},
@@ -60,7 +70,7 @@ describe("syncState", () => {
     let onLeave = (key, current, leftPres) => {
       left[key] = {current: current, leftPres: leftPres}
     }
-    Presence.syncState(state, newState, onJoin, onLeave)
+    state = Presence.syncState(state, newState, onJoin, onLeave)
     assert.deepEqual(state, newState)
     assert.deepEqual(joined, {
       u3: {current: {metas: [{id: 3, phx_ref: "3"}]},
@@ -74,7 +84,10 @@ describe("syncDiff", () => {
   it("syncs empty state", () => {
     let joins = {u1: {metas: [{id: 1, phx_ref: "1"}]}}
     let state = {}
-    Presence.syncDiff(state, {
+    Presence.syncDiff(state, {joins: joins, leaves: {}})
+    assert.deepEqual(state, {})
+
+    state = Presence.syncDiff(state, {
       joins: joins,
       leaves: {}
     })
@@ -83,7 +96,7 @@ describe("syncDiff", () => {
 
   it("removes presence when meta is empty and adds additional meta", () => {
     let state = fixtures.state()
-    Presence.syncDiff(state, {joins: fixtures.joins(), leaves: fixtures.leaves()})
+    state = Presence.syncDiff(state, {joins: fixtures.joins(), leaves: fixtures.leaves()})
 
     assert.deepEqual(state, {
       u1: {metas: [{id: 1, phx_ref: "1"}, {id: 1, phx_ref: "1.2"}]},
@@ -95,7 +108,7 @@ describe("syncDiff", () => {
     let state = {
       u1: {metas: [{id: 1, phx_ref: "1"}, {id: 1, phx_ref: "1.2"}]}
     }
-    Presence.syncDiff(state, {joins: {}, leaves: {u1: {metas: [{id: 1, phx_ref: "1"}]}}})
+    state = Presence.syncDiff(state, {joins: {}, leaves: {u1: {metas: [{id: 1, phx_ref: "1"}]}}})
 
     assert.deepEqual(state, {
       u1: {metas: [{id: 1, phx_ref: "1.2"}]},