package.json snippet

{
    "scripts":
        "test": "karma start",
        "karma": "karma"
    }
}

There are two types of npm scripts, and the command to run each is slightly different. The first type of npm scripts are "pre-recognized" scripts. These scripts are automatically recognized by npm and don't need a special prefix (as you will see for the other type) to run them. The other type of scripts are "custom" scripts. These scripts aren't pre-recognized by npm and have to be prefixed by a special command to run them. There are a list of pre-recognized scripts in the remarks section.

To run pre-recognized scripts:

npm start or npm test

To run custom scripts you need to use the run command:

npm run karma

The npm scripts are commands that npm will run for you when called with the proper arguments. The power and sense of this is to NOT install the npm packages globally poluting your environment.

The difference between pre-recognized and custom scripts relies on the run word between the tags, custom scripts will need the run between npm and the script name

Based on this we can differenciate and create different tasks or scripts to be run with npm.

Given the following example on the package.json file:

{
  "name": "MyApp",
  "version": "1.0.0",
  "description": "",
  "main": "app.js",
  "scripts": {
    "test": "mocha --recursive ./tests/",
    "test:watch": "npm run test -- -w",
    "start": "nodemon --inspect ./app.js",
    "build": "rm -rf ./dist/ && gulp build"
  }
...
}

We can see different tasks to be run:

• npm test Would work fine as it is a pre-recognized script

• npm run test Would work fine as it is a valid way to execute a npm script

• npm run test:watch Would work also, and it's calling npm run test inside itself

• npm run build Would before running gulp build delete the dist folder that is in the directory (assuming you are in Linux or the command rm is recognized)