fix mixin issue (#5514)

src/core/instance/init.js

@@ -115,24 +115,27 @@ export function resolveConstructorOptions (Ctor: Class<Component>) {
 function resolveModifiedOptions (Ctor: Class<Component>): ?Object {
   let modified
   const latest = Ctor.options
+  const extended = Ctor.extendOptions
   const sealed = Ctor.sealedOptions
   for (const key in latest) {
     if (latest[key] !== sealed[key]) {
       if (!modified) modified = {}
-      modified[key] = dedupe(latest[key], sealed[key])
+      modified[key] = dedupe(latest[key], extended[key], sealed[key])
     }
   }
   return modified
 }
 
-function dedupe (latest, sealed) {
+function dedupe (latest, extended, sealed) {
   // compare latest and sealed to ensure lifecycle hooks won't be duplicated
   // between merges
   if (Array.isArray(latest)) {
     const res = []
     sealed = Array.isArray(sealed) ? sealed : [sealed]
+    extended = Array.isArray(extended) ? extended : [extended]
     for (let i = 0; i < latest.length; i++) {
-      if (sealed.indexOf(latest[i]) < 0) {
+      // push original options and not sealed options to exclude duplicated options
+      if (extended.indexOf(latest[i]) >= 0 || sealed.indexOf(latest[i]) < 0) {
         res.push(latest[i])
       }
     }

test/unit/features/global-api/mixin.spec.js

@@ -141,4 +141,25 @@ describe('Global API: mixin', () => {
     })
     expect(spy).toHaveBeenCalledWith('hello')
   })
+
+  // vue-class-component#87
+  it('should not drop original lifecycle hooks', () => {
+    const base = jasmine.createSpy('base')
+
+    const Base = Vue.extend({
+      beforeCreate: base
+    })
+
+    const injected = jasmine.createSpy('injected')
+
+    // inject a function
+    Base.options.beforeCreate = Base.options.beforeCreate.concat(injected)
+
+    Vue.mixin({})
+
+    new Base({})
+
+    expect(base).toHaveBeenCalled()
+    expect(injected).toHaveBeenCalled()
+  })
 })