add change event

src/client/updateClientMetaInfo.js

@@ -28,6 +28,10 @@ if (typeof window !== 'undefined' && window !== null) {
 export default function updateClientMetaInfo (newInfo, $root) {
   // if this is not a server render, then update
   if (htmlTag.getAttribute(SERVER_RENDERED_ATTRIBUTE) === null) {
+    // initialize tracked changes
+    const addedTags = {}
+    const removedTags = {}
+
     // update the title
     updateTitle(newInfo.title)
 
@@ -40,14 +44,18 @@ export default function updateClientMetaInfo (newInfo, $root) {
     // update tags
     for (let i = 0, len = tags.length; i < len; i++) {
       const tag = tags[i]
-      updateTags(tag, newInfo[tag], headTag)
+      const { oldTags, newTags } = updateTags(tag, newInfo[tag], headTag)
+      if (newTags.length) {
+        addedTags[tag] = newTags
+        removedTags[tag] = oldTags
+      }
+    }
+
+    // emit event
+    if (typeof newInfo.changed === 'function') {
+      newInfo.changed(newInfo, addedTags, removedTags)
     }
   } else {
     htmlTag.removeAttribute(SERVER_RENDERED_ATTRIBUTE)
   }
-
-  // HACK: since we're performing DOM side effects, we can't rely on
-  // Vue.nextTick in our tests. This event helps keep the test suite
-  // free of setTimeout clutter
-  $root.$emit('vue-meta-update')
 }

src/shared/getMetaInfo.js

@@ -15,7 +15,7 @@ export default function getMetaInfo (component) {
   for (let key in info) {
     if (info.hasOwnProperty(key)) {
       const value = info[key]
-      if (typeof value === 'function') {
+      if (typeof value === 'function' && key !== 'changed') {
         info[key] = value()
       }
     }