Run function in script from command line (Node JS)

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 };

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

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

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());'

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.

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...
}

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

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.

Following on from the other answers here, if you wanted to make this reusable you could create a script as follows:

// rn-fn.js
const [, , filePath, fn, ...args] = process.argv;
import(filePath).then((mod) => mod[fn](...args));

Then as an example:

// hello.js
export function hello(str) {
  console.log(`hello ${str}`)
}

Running:

node ./rn-fn.js ./hello.js hello world

at the command line should then return

hello world

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're running node from command line, you can use eval (yeah I know it's not recommended but honestly there's no risk here). I personally put "fn_" at the front to distinguish function calls, but you can just skip the if statement (and the string replace) entirely if you wish to.

// callFromScript.js

let args = process.argv.slice(2);

if (args[0].startsWith("fn_")) {
    let methodName = args[0].replace("fn_", "");
    let methodArgs = args.slice(1);
    methodArgs.forEach((arg, index) => {
        let isObjectLike = arg.startsWith('{') || arg.startsWith('[');
        if (!isObjectLike && isNaN(arg)) {
            methodArgs[index] = `"${arg}"`;
        }
    });
    let methodSyntax = `${methodName}(${methodArgs.join(',')})`;
    console.log(methodSyntax);

    try {
        eval(methodSyntax);
    } catch (error) {
        throw error;
    }
}

function test() {
    console.log("Success");
}

function testArgs(a1, a2, a3, a4) {
    console.log(a1, a2, a3, a4);
}

node callFromScript.js fn_test
node callFromScript.js fn_testArgs 1 text "[]" {}

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