feat: add constructor hint

Author: Hazlank

Diff for: src/history/base.js

@@ -146,8 +146,10 @@ export class History {
             cb(err)
           })
         } else {
-          warn(false, 'uncaught error during route navigation:')
-          console.error(err)
+          if (process.env.NODE_ENV !== 'production') {
+            warn(false, 'uncaught error during route navigation:')
+            console.error(err)
+          }
         }
       }
       onAbort && onAbort(err)

Diff for: src/index.js

@@ -39,6 +39,9 @@ export default class VueRouter {
   afterHooks: Array<?AfterNavigationHook>
 
   constructor (options: RouterOptions = {}) {
+    if (process.env.NODE_ENV !== 'production') {
+      warn(this instanceof VueRouter, `Router must be called with the new operator.`)
+    }
     this.app = null
     this.apps = []
     this.options = options

Diff for: src/util/warn.js

@@ -7,7 +7,7 @@ export function assert (condition: any, message: string) {
 }
 
 export function warn (condition: any, message: string) {
-  if (process.env.NODE_ENV !== 'production' && !condition) {
+  if (!condition) {
     typeof console !== 'undefined' && console.warn(`[vue-router] ${message}`)
   }
 }