Run function in script from command line (Node JS)

I'm writing a web app in Node. If I've got some JS file db.js with a function init in it how could I call that function from the command line?

No comment on why you want to do this, or what might be a more standard practice: here is a solution to your question.... Keep in mind that the type of quotes required by your command line may vary.

In your db.js, export the init function. There are many ways, but for example:

module.exports.init = function () {
  console.log('hi');
};

Then call it like this, assuming your db.js is in the same directory as your command prompt:

node -e 'require("./db").init()'

To other readers, the OP's init function could have been called anything, it is not important, it is just the specific name used in the question.

As per the other answers, add the following to someFile.js

module.exports.someFunction = function () {
  console.log('hi');
};

You can then add the following to package.json

"scripts": {
   "myScript": "node -e 'require(\"./someFile\").someFunction()'"
}

From the terminal, you can then call

npm run myScript

I find this a much easier way to remember the commands and use them

Update 2020 - CLI

As @mix3d pointed out you can just run a command where file.js is your file and someFunction is your function optionally followed by parameters separated with spaces

npx run-func file.js someFunction "just some parameter"

That's it.

file.js called in the example above

const someFunction = (param) => console.log('Welcome, your param is', param)

// exporting is crucial
module.exports = { someFunction }

More detailed description

Run directly from CLI (global)

Install

npm i -g run-func

Usage i.e. run function "init", it must be exported, see the bottom

run-func db.js init

or

Run from package.json script (local)

Install

npm i -S run-func

Setup

"scripts": {
   "init": "run-func db.js init"
}

Usage

npm run init

Params

Any following arguments will be passed as function parameters init(param1, param2)

run-func db.js init param1 param2

Important

the function (in this example init) must be exported in the file containing it

module.exports = { init };

or ES6 export

export { init };

Try make-runnable.

In db.js, add require('make-runnable'); to the end.

Now you can do:

node db.js init

Any further args would get passed to the init method, in the form of a list or key-value pairs.

Sometimes you want to run a function via CLI, sometimes you want to require it from another module. Here's how to do both.

// file to run
const runMe = () => {}
if (require.main === module) {
  runMe()
} 
module.exports = runMe

This one is dirty but works :)

I will be calling main() function from my script. Previously I just put calls to main at the end of script. However I did add some other functions and exported them from script (to use functions in some other parts of code) - but I dont want to execute main() function every time I import other functions in other scripts.

So I did this, in my script i removed call to main(), and instead at the end of script I put this check:

if (process.argv.includes('main')) {
   main();
}

So when I want to call that function in CLI: node src/myScript.js main

simple way:

let's say you have db.js file in a helpers directory in project structure.

now go inside helpers directory and go to node console

 helpers $ node

2) require db.js file

> var db = require("./db")

3) call your function (in your case its init())

> db.init()

hope this helps

If you turn db.js into a module you can require it from db_init.js and just: node db_init.js.

db.js:

module.exports = {
  method1: function () { ... },
  method2: function () { ... }
}

db_init.js:

var db = require('./db');

db.method1();
db.method2();

I do a IIFE, something like that:

(() => init())();

this code will be executed immediately and invoke the init function.

Updated for 2022 - If you've switched to ES Modules, you can't use the require tricks, you'd need to use dynamic imports:

node -e 'import("./db.js").then(dbMod => dbMod.init());'

or with the --experimental-specifier-resolution=node flag:

node --experimental-specifier-resolution=node -e 'import("./db").then(dbMod => dbMod.init());'

maybe this method is not what you mean, but who knows it can help

index.js

const arg = process.argv.splice(2);

function printToCli(text){
    console.log(text)
}

switch(arg[0]){
    case "--run":
        printToCli("how are you")
    break;
    default: console.log("use --run flag");
}

and run command node . --run

command line

probuss-MacBook-Air:fb_v8 probus$ node . --run
how are you
probuss-MacBook-Air:fb_v8 probus$ 

and you can add more arg[0] , arg[1], arg[2] ... and more

for node . --run -myarg1 -myarg2

Inspired by https://github.com/DVLP/run-func/blob/master/index.js

I create https://github.com/JiangWeixian/esrua

if file index.ts

export const welcome = (msg: string) => {
  console.log(`hello ${msg}`)
}

just run

esrua ./index.ts welcome -p world

will output hello world

If you want to include environment variables from your .env files, you can use env-cmd:

npx env-cmd node -e 'require("./db").init()'

If you want run a specific function in the file too, use run-func:

npx env-cmd npx run-func db.js init someArg

Or, to provide an argument for the accepted answer you'd have to do something like:

npx env-cmd node -e 'require("./db").init(someArg)'

Writing/updating an expression here is less explicit (so easier to miss when you're checking back, for example) than providing different arguments to the commands, so I recommend using env-cmd with run-func.

Note: I also usually add --experimental-modules on the end when necessary.

You can also run TypeScript with ts-node similar to @LeeGoddard answer.
In my case, I wanted to use app and init separately for testing purposes.

// app.ts

export const app = express();

export async function init(): Promise<void> {
   // app init logic...
}

npx ts-node -e 'require("./src/app").init();'
npx ts-node -e 'import("./src/app").then(a => a.init());' // esmodule

If your file just contains your function, for example:

myFile.js:

function myMethod(someVariable) {
    console.log(someVariable)
}

Calling it from the command line like this nothing will happen:

node myFile.js

But if you change your file:

myFile.js:

myMethod("Hello World");

function myMethod(someVariable) {
    console.log(someVariable)
}

Now this will work from the command line:

node myFile.js