Commands

Part of the Node.js Basics section of Coddy's Node.js journey. Lesson 4 of 33.

The tool will do several things, and the first word says which.

Destructuring takes the first word and gathers the rest into an array:

// node calc.js double 4
const [action, ...rest] = process.argv.slice(2);
if (action === 'double') {
    console.log(Number(rest[0]) * 2);
}

action is the first word and rest holds every word after it. rest.join(' ') puts those words back into one string. A chain of if and else if picks what to do. A final else catches every word you did not plan for, a typo included.

Challenge

Easy

Your tool will do several jobs, and the first word after node notes.js says which one. Now it learns two commands, add and list, and a reply for any word it does not know.

In notes.js, replace both starter lines. Split the words after node notes.js into the command, which is the first word, and the rest, which is every other word.
Pick what to do with one if, else if, else chain on the command. Each command prints exactly one line:
- add prints Adding: followed by the rest of the words, joined with spaces. node notes.js add Buy milk prints Adding: Buy milk.
- list prints No notes yet. Notes are not saved anywhere yet; that comes in chapter 3.
- Any other first word prints Unknown command: followed by that first word only. node notes.js remove 3 prints Unknown command: remove, without the 3.
Nothing else may print. If last lesson's line that prints Adding: stays outside the chain, it runs for every command, list prints two lines, and the checks fail.

All three cases end normally, with exit code 0. The next lesson turns unknown commands into errors.

Try it: type each of these in the box after $ node notes.js and press Enter.

add Buy milk shows Adding: Buy milk.
list shows No notes yet.
remove 3 shows Unknown command: remove.
List, with a capital L, shows Unknown command: List. JavaScript compares text letter by letter, capitals included, so List is not list.

Try it yourself

// Your notes tool starts here.
const args = process.argv.slice(2);
console.log(`Adding: ${args.slice(1).join(' ')}`);

All lessons in Node.js Basics

1Running JavaScript on Node

Hello, Node Reading the Command Command-Line ArgumentsCommands Project lesson

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