feat: add warn

src/apis/index.ts

@@ -30,3 +30,4 @@ export { useCSSModule } from './useCssModule'
 export { createApp } from './createApp'
 export { nextTick } from './nextTick'
 export { createElement as h } from './createElement'
+export { warn } from './warn'

src/apis/warn.ts

@@ -0,0 +1,12 @@
+import { getCurrentInstance } from '../runtimeContext'
+import { warn as vueWarn } from '../utils'
+
+/**
+ * Displays a warning message (using console.error) with a stack trace if the
+ * function is called inside of active component.
+ *
+ * @param message warning message to be displayed
+ */
+export function warn(message: string) {
+  vueWarn(message, getCurrentInstance())
+}

src/env.d.ts

@@ -19,7 +19,7 @@ declare module 'vue/types/vue' {
   interface VueConstructor {
     observable<T>(x: any): T
     util: {
-      warn(msg: string, vm?: Vue)
+      warn(msg: string, vm?: Vue | null)
       defineReactive(
         obj: Object,
         key: string,

src/utils/utils.ts

@@ -83,7 +83,7 @@ export function isUndef(v: any): boolean {
   return v === undefined || v === null
 }
 
-export function warn(msg: string, vm?: Vue) {
+export function warn(msg: string, vm?: Vue | null) {
   Vue.util.warn(msg, vm)
 }
 

test/apis/warn.spec.js

@@ -0,0 +1,32 @@
+const Vue = require('vue/dist/vue.common.js')
+const { warn: apiWarn } = require('../../src')
+
+describe('api/warn', () => {
+  beforeEach(() => {
+    warn = jest.spyOn(global.console, 'error').mockImplementation(() => null)
+  })
+  afterEach(() => {
+    warn.mockRestore()
+  })
+
+  it('can be called inside a component', () => {
+    new Vue({
+      setup() {
+        apiWarn('warned')
+      },
+      template: `<div></div>`,
+    }).$mount()
+
+    expect(warn).toHaveBeenCalledTimes(1)
+    expect(warn.mock.calls[0][0]).toMatch(
+      /\[Vue warn\]: warned[\s\S]*\(found in <Root>\)/
+    )
+  })
+
+  it('can be called outside a component', () => {
+    apiWarn('warned')
+
+    expect(warn).toHaveBeenCalledTimes(1)
+    expect(warn).toHaveBeenCalledWith('[Vue warn]: warned')
+  })
+})