1npm install nodemon --save-dev

1npm install nodemon 
2
3in your package.json add in the scripts 
4"command":"nodemon mainfile.js"
5
6eg
7{
8  "name": "abc",
9  "version": "0.0.1",
10  "description": "my server",
11  "scripts": {
12    "start": "nodemon my_file.js"
13  },
14  "devDependencies": {
15    "nodemon": "~1.3.8",
16  },
17  "dependencies": {
18
19  }
20}
21

1npm install -g nodemon

1npm install -g nodemon

1nodemon --exec npm run dev:test