02 Values and types

Goal: learn the minimum JavaScript vocabulary you'll use throughout this ladder — variables, strings, numbers, booleans, arrays, and objects.

Variables

Use const for values that won't be reassigned and let for values that will.

const name = "Alice";      // string — fixed
let score = 0;             // number — will change

Strings and template literals

const item = "buy milk";
const msg = `Todo: ${item}`;   // template literal
console.log(msg);              // Todo: buy milk

Numbers and booleans

const count = 3;
const active = true;
console.log(count + 1);   // 4
console.log(!active);     // false

Arrays

An ordered list of values. You'll use arrays to hold your todos.

const todos = [];
todos.push("buy milk");
todos.push("walk dog");
console.log(todos.length);   // 2
console.log(todos[0]);       // buy milk

Objects

A key-value record. Each todo will be an object with text and done fields.

const todo = { text: "buy milk", done: false };
console.log(todo.text);   // buy milk

Checkpoint

Create types.js and run it:

// types.js
const todos = [
  { text: "buy milk", done: false },
  { text: "walk dog", done: false },
];
const first = todos[0];
console.log(`${todos.length} todos — first: ${first.text}`);

node types.js   # 2 todos — first: buy milk

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Next: 03 Functions and modules