Node.js, accept arguments from the command line

You can pass any number of arguments when invoking a Node.js application using

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node app.js

Arguments can be standalone or have a key and a value.

For example:

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node app.js joe

or

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node app.js name=joe

This changes how you will retrieve this value in the Node.js code.

The way you retrieve it is using the process object built into Node.js.

It exposes an argv property, which is an array that contains all the command line invocation arguments.

The first element is the full path of the node command.

The second element is the full path of the file being executed.

All the additional arguments are present from the third position going forward.

You can iterate over all the arguments (including the node path and the file path) using a loop:

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process.argv.forEach((val, index) => {
  console.log(`${index}: ${val}`);
});

You can get only the additional arguments by creating a new array that excludes the first 2 params:

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

If you have one argument without an index name, like this:

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node app.js joe

you can access it using

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const args = process.argv.slice(2);
args[0];

In this case:

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node app.js name=joe

args[0] is name=joe, and you need to parse it. The best way to do so is by using the minimist library, which helps dealing with arguments:

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const args = require('minimist')(process.argv.slice(2));

args.name; // joe

Install the required minimist package using npm (lesson about the package manager comes later on).

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npm install minimist

This time you need to use double dashes before each argument name:

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node app.js --name=joe