JS server not recognized, continuing with build

问题

Environment

Windows 10

Npm 5.5.1

react-native-cli 2.0.1

react-native 0.50.3

Genymotion Google Nexus 7 - 6.0.0 API 23

Android stuff:

Sdk Version: 26

buildToolsVersion '26.0.2'

TargetsdkVersion: 26

compile "com.android.support:appcompat-v7:26.0.2"

I have run npm start --reset-cache as well as react-native start --reset-cache but I keep getting the JS server not recognized, continuing with build. This prevents the packager bundling the assets before running on my Emulator.

I have followed solution 1 on this post:

https://github.com/facebook/react-native/issues/9136#issuecomment-306486102

as well as this one:

Unable to recognize JS server

I started this project with react-native init APP. Already having trouble building it with this error. checking serval posts on here and other sites mentioned using npm cache clean and react-native start --reset-cache and that did not seem to help I keep getting the same error. I had it running smoothly at one time but I altered an npm package and I think I broke it again. any help would be appreciated. I also updated the gradle version and synced that into the project

Heres some screenshots of what I am experiencing...

** CODE **

index.js

import { AppRegistry } from 'react-native';
import App from './App';

AppRegistry.registerComponent('hihi', () => App);

App.js /** * Sample React Native App * https://github.com/facebook/react-native * @flow */

import React, { Component } from 'react';
import {
  Platform,
  StyleSheet,
  Text,
  View
} from 'react-native';

const instructions = Platform.select({
  ios: 'Press Cmd+R to reload,\n' +
    'Cmd+D or shake for dev menu',
  android: 'Double tap R on your keyboard to reload,\n' +
    'Shake or press menu button for dev menu',
});

export default class App extends Component<{}> {
  render() {
    return (
      <View style={styles.container}>
        <Text style={styles.welcome}>
          Welcome to React Native!
        </Text>
        <Text style={styles.instructions}>
          To get started, edit App.js
        </Text>
        <Text style={styles.instructions}>
          {instructions}
        </Text>
      </View>
    );
  }
}

const styles = StyleSheet.create({
  container: {
    flex: 1,
    justifyContent: 'center',
    alignItems: 'center',
    backgroundColor: '#F5FCFF',
  },
  welcome: {
    fontSize: 20,
    textAlign: 'center',
    margin: 10,
  },
  instructions: {
    textAlign: 'center',
    color: '#333333',
    marginBottom: 5,
  },
});

app.json

{
  "name": "hihi",
  "displayName": "hihi"
}

.babelrc

{
  "presets": ["react-native"]
}

package.json

{
    "name": "hihi",
    "version": "0.0.1",
    "private": true,
    "scripts": {
        "start": "node node_modules/react-native/local-cli/cli.js start",
        "test": "jest"
    },
    "dependencies": {
        "react": "16.0.0",
        "react-native": "0.50.3",
        "watchman": "^0.1.8"
    },
    "devDependencies": {
        "babel-jest": "21.2.0",
        "babel-polyfill": "^6.26.0",
        "babel-preset-es2015": "^6.24.1",
        "babel-preset-react-native": "4.0.0",
        "babel-register": "^6.26.0",
        "jest": "21.2.1",
        "react-test-renderer": "16.0.0"
    },
    "jest": {
        "preset": "react-native"
    }
}

UPDATE UPDATE

I figured it out, it was a combination of the suggestions on this post and this solution as well:

Could not find com.android.tools.build:gradle:3.0.0-alpha1 in circle ci

I needed to include google() in both locations as well as the solution of switching it to port 8082 and enabling that port on the emulator. THANK YOU ALL SO MUCH FOR YOUR HELP!!! =)

回答1:

Steps that helped me in similar case:

1. Running packager on port different than 8081: react-native start --port 8082 --reset-cache
2. Running command react-native run-android --port 8082 in second Command Prompt window.
3. After error screen appear clicking Ctrl + M.
4. Clicking Dev Settings button at the bottom.
5. Clicking Debug server host & port for device button.
6. Writing localhost:8082 and clicking OK button.
7. Again running command react-native run-android --port 8082

回答2:

I had this issue when I had another process running on port 8081.

1. Find the process lsof -i tcp:8081
2. Get the PID, in my case 25120
3. Kill the process: kill -9 25120
4. Start React Native Again

回答3:

In my case (had the same error) I simply checked netstat in win CMD (check for reference). My problem was running another instance on port :8081 so I had to kill the bastard.

1. Close all running local server instances.
2. Check link for reference on killing :8081 proccess on Windows
3. Rebuild & rerun project.
4. Profit

回答4:

Just changing port doesnt solve the issue, instead it creates more unless you also change the port from the device itself.

First, confirm if its the case:

$> netstat -aon|findstr “8081”

Now change it to run from a new Default Port

a) Change env variable on windows to set a new port for RN:

$> SET RCT_METRO_PORT=8083

This is used in RN to use as the default port, and if not set it defaults to 8081

b) Remove old reverse:

$> adb reverse –remove-all

c) Set new reverse port for the adb device:

$> adb reverse tcp:8083 tcp:8083

d) Change Dev Settings on the device from the default 8081 to 8083.

Run the app and then run input keyevent 82, now select Dev Settings > Debug Server host … > enter new url: localhost:8083

build and run again

回答5:

Try to turn off a local server program like MAMP, WAMP, OpenServer e.t.c. They can use the 8081 port.

来源：https://stackoverflow.com/questions/47341120/js-server-not-recognized-continuing-with-build