feat: renderError

flow/options.js

@@ -33,7 +33,8 @@ declare type ComponentOptions = {
   // DOM
   el?: string | Element;
   template?: string;
-  render: () => VNode;
+  render: (h: () => VNode) => VNode;
+  renderError?: (h: () => VNode, err: Error) => VNode;
   staticRenderFns?: Array<() => VNode>;
   // lifecycle
   beforeCreate?: Function;

src/core/instance/render.js

@@ -78,8 +78,15 @@ export function renderMixin (Vue: Class<Component>) {
       vnode = render.call(vm._renderProxy, vm.$createElement)
     } catch (e) {
       handleError(e, vm, `render function`)
-      // return previous vnode to prevent render error causing blank component
-      vnode = vm._vnode
+      // return error render result,
+      // or previous vnode to prevent render error causing blank component
+      if (process.env.NODE_ENV !== 'production') {
+        vnode = vm.$options.renderError
+          ? vm.$options.renderError.call(vm._renderProxy, vm.$createElement, e)
+          : vm._vnode
+      } else {
+        vnode = vm._vnode
+      }
     }
     // return empty vnode in case the render function errored out
     if (!(vnode instanceof VNode)) {

test/unit/features/error-handling.spec.js

@@ -96,7 +96,9 @@ describe('Error handling', () => {
     expect(args[1]).toBe(vm.$refs.child) // vm
     expect(args[2]).toContain('render function') // description
 
-    assertRootInstanceActive(vm).then(done)
+    assertRootInstanceActive(vm).then(() => {
+      Vue.config.errorHandler = null
+    }).then(done)
   })
 })
 

test/unit/features/options/renderError.spec.js

@@ -0,0 +1,28 @@
+import Vue from 'vue'
+
+describe('Options renderError', () => {
+  it('should be used on render errors', done => {
+    Vue.config.errorHandler = () => {}
+    const vm = new Vue({
+      data: {
+        ok: true
+      },
+      render (h) {
+        if (this.ok) {
+          return h('div', 'ok')
+        } else {
+          throw new Error('no')
+        }
+      },
+      renderError (h, err) {
+        return h('div', err.toString())
+      }
+    }).$mount()
+    expect(vm.$el.textContent).toBe('ok')
+    vm.ok = false
+    waitForUpdate(() => {
+      expect(vm.$el.textContent).toBe('Error: no')
+      Vue.config.errorHandler = null
+    }).then(done)
+  })
+})