library can now receive message to jump back in time

package/index.js

@@ -1,13 +1,19 @@
 const snapShot = [];
+const mode = { jumping: false };
+
+const linkState = require('./linkState')(snapShot, mode);
+const timeJump = require('./timeJump')(snapShot, mode);
+
+const getShot = () => snapShot.map(({ component }) => component.state);
 
 window.addEventListener('message', ({ data: { action, payload } }) => {
   if (action === 'jumpToSnap') {
-    console.log('snap received from chrome', payload);
+    timeJump(payload);
   }
 });
 
-const linkState = require('./linkState')(snapShot);
-
 module.exports = {
   linkState,
+  timeJump,
+  getShot,
 };

package/linkState.js

@@ -1,29 +1,46 @@
 // links component state to library
 // changes the setState method to also update our snapshot
 
-module.exports = (snapShot) => {
+module.exports = (snapShot, mode) => {
+  // send message to window containing component states
+  // unless library is currently jumping through time
   function sendSnapShot() {
-    const payload = snapShot.map(comp => comp.state);
+    if (mode.jumping) return;
+    const payload = snapShot.map(({ component }) => component.state);
     window.postMessage({
       action: 'recordSnap',
       payload,
     });
   }
 
   return (component) => {
-    snapShot.push(component);
+    // make a copy of setState
+    const oldSetState = component.setState.bind(component);
 
-    sendSnapShot();
+    // convert setState to promise
+    const setStateAsync = (state) => {
+      return new Promise(resolve => oldSetState(state, resolve));
+    };
 
-    const oldSetState = component.setState.bind(component);
+    // add component to snapshot
+    snapShot.push({ component, setStateAsync });
 
+    let first = true;
     function newSetState(state, callback = () => { }) {
+      // if setState is being called for the first time, this conditional sends the initial snapshot
+      if (first) {
+        first = false;
+        sendSnapShot();
+      }
+
+      // continue normal setState functionality, except add sending message middleware
       oldSetState(state, () => {
         sendSnapShot();
         callback();
       });
     }
 
+    // replace component's setState so developer doesn't change syntax
     component.setState = newSetState;
   };
 };

package/timeJump.js

@@ -0,0 +1,9 @@
+module.exports = (snapShot, mode) => {
+  return (newSnapShot) => {
+    mode.jumping = true;
+    newSnapShot.forEach(async (state, i) => {
+      await snapShot[i].setStateAsync(state);
+    });
+    mode.jumping = false;
+  };
+};