JSON Text and Values

Part of the Node.js Basics section of Coddy's Node.js journey. Lesson 11 of 33.

A file holds text. Your program often needs an array instead. JSON is a text format for values such as arrays, objects, numbers and strings. The quotes around the entire value below make it text, even though its contents look like an array.

const text = '[10,20]';
const scores = JSON.parse(text);
console.log(scores[0]); // 10
console.log(scores.length); // 2

JSON.parse reads the text and returns the value it describes. Count the resulting items, not the characters in the text. JSON strings and object keys use double quotes.

Challenge

Easy

For this exercise, Run executes node practice.js. The notes tool returns in Reading a File. The starter treats JSON text as if it were an array.

Parse text into an array. Print its first item and its item count on separate lines. With no arguments, expect Buy milk then 3. Try the argument '["Walk","Read"]': expect Walk then 2.

Try it yourself

const text = process.argv[2] ?? '["Buy milk","Call Ada","Read"]';
console.log(text[0]);
console.log(text.length);

All lessons in Node.js Basics

1Running JavaScript on Node

Hello, Node Reading the Command Command-Line Arguments Commands

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 ValuesReading a File Writing JSON Text Writing a File Removing a Note

Handling Errors

6Project: Search and Tags