Command-Line Arguments

Part of the Node.js Basics section of Coddy's Node.js journey. Lesson 3 of 33.

A notes tool has to know what you typed after its name.

process.argv is an array of the words in the command: the path to Node, the path to your file, then your words. slice(2) keeps only yours.

// node greet.js Ada
const args = process.argv.slice(2);
console.log(`Hello, ${args[0]}!`);

node greet.js Ada prints Hello, Ada!. Each word arrives as its own string, so node greet.js Ada Lovelace gives args the value ['Ada', 'Lovelace']. To put words back into one string, use join(' '): ['Ada', 'Lovelace'].join(' ') is 'Ada Lovelace'. Quotes keep words together: node greet.js "Ada Lovelace" gives one string.

Challenge

Easy

Your notes tool needs to know what you typed after node notes.js. Here it reads a note from the command and repeats it back.

In notes.js, read the words typed after node notes.js with process.argv. The first word is the command, add. For now it is always add. Every word after it is the note.
The note's words arrive as separate strings. Put them back together into one string, with one space between words.
Replace the starter's console.log('Adding:') line. Print one line: Adding: followed by the note.

For node notes.js add Buy milk the program prints:

Adding: Buy milk

For node notes.js add Call Ada tonight it prints:

Adding: Call Ada tonight

Put one space after Adding:.

Try it: in the terminal, type add Buy milk in the box after $ node notes.js and press Enter. You see Adding: Buy milk. Then type a note of your own, such as add Call Ada tonight. Last, type only add: you see Adding: with nothing after it, because there is no note. That is fine for now.

Try it yourself

// Your notes tool starts here.
// node notes.js add Buy milk should print: Adding: Buy milk
console.log('Adding:');

Test yourself

This lesson includes a short quiz. Start the lesson to answer it and track your progress.

All lessons in Node.js Basics

1Running JavaScript on Node

Hello, Node Reading the CommandCommand-Line ArgumentsCommands

Errors and Exit Codes

Environment Variables

4Asynchronous Node

Using a Callback Result Callbacks A Promise Result When a Promise Fails Promises Waiting for a Value Async and Await Two Independent Reads Promise.all The Event Loop Timers

2Modules

5Events, Input and Packages

Listen Before Emitting Event Emitters Reading Input

package.json

3Files

JSON Text and Values Reading a File Writing JSON Text Writing a File Removing a Note

Handling Errors

6Project: Search and Tags