make sure plugin install only once

Author: ustbhuangyi

src/debug.js

@@ -1,13 +1,13 @@
 export function warn(msg) {
-  console.error(`[create-api warn]: ${msg}`)
+  console.error(`[vue-create-api warn]: ${msg}`)
 }
 
 export function assert(condition, msg) {
   if (!condition) {
-    throw new Error(`[create-api error]: ${msg}`)
+    throw new Error(`[vue-create-api error]: ${msg}`)
   }
 }
 
 export function tip(msg) {
-  console.warn(`[create-api tip]: ${msg}`)
+  console.warn(`[vue-create-api tip]: ${msg}`)
 }

src/index.js

@@ -1,8 +1,15 @@
 import { camelize, escapeReg, isBoolean } from './util'
-import { assert } from './debug'
+import { assert, warn } from './debug'
 import apiCreator from './creator'
 
+let installed = false
+
 function install(Vue, options = {}) {
+  if (installed) {
+    warn('[vue-create-api] already installed. Vue.use(CreateAPI) should be called only once.')
+    return
+  }
+  installed = true
   const {componentPrefix = '', apiPrefix = '$create-'} = options
 
   Vue.createAPI = function (Component, events, single) {