JS server not recognized, continuing with build

Question

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

Answer 1

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

Answer 2

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

Answer 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

Answer 4

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

Answer 5

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