NPM - Scripts - How Do They Work?

Question

I cant get my head around how scripts are running within package.json & would appreciate some insight for us newbies.

Is it the case that they are bash scripts that are run by node having loaded the various dependencies ?

If yes, then how does it process the javascript code?

Answer 1

Is it the case that they are bash scripts

yes

that are run by node

no, they are run by sh .

having loaded the various dependencies?

no, no js files are loaded, the only thing npm does for you is to prepare the environment . Among other things, it adds ./node_modules/.bin to PATH so you can invoke installed modules immediately.

When you run npm run-script whatever , this is what npm does:

• reads the corresponding command line from package.json
• prepares the environment
• invokes sh (or comspec on win) and gives it the command and the env. No big magic here.

Answer 2

This may not be 100% accurate so I implore other, more qualifies, experts to chime in.

NPM is a program, installed as part of the Node.JS environment. It's two main uses (as describe here ) are for searching for node.js packages and installing node.js packages.

However, NPM is also capable of understanding "simple" (a relative term) scripts.

When you write a script in your package.json, and issue the NPM command, say "npm start", NPM will read and interpret the script. NPM then searches your node_modules structure for the accompanying binary and executes that binary with the necessary start parameters.

An example would be

"test": "mocha --reporter spec test"

when you issue "npm test", NPM will look for the mocha binary in your node_modules structure. NPM finds mocha initiates the call, passing the reporter command arg (--reporter spec) and the name of the file to be read and executed for the test.