Modern & Async JavaScript

Modern syntax for creating strings and safely accessing values.

Term / Syntax	Name	Description	Example
template literal	Interpolated String	Creates strings with embedded expressions.	const message = `Hello, ${name}!`;
?.	Optional Chaining	Safely accesses a property by returning undefined if the preceding value is null or undefined.	user.profile?.avatar

Creating object templates, instances, and inheritance relationships with classes.

Term / Syntax	Name	Description	Example
class	Class Declaration	Defines a template for creating objects with related properties and methods.	class User { constructor(name) { this.name = name; } }
constructor()	Instance Initialization	Initializes a new object when an instance of a class is created.	constructor(name) { this.name = name; }
new	Create Instance	Creates a new object instance by calling a constructor or class.	const user = new User("Jennifer");
extends	Class Inheritance	Creates a class that inherits properties and methods from another class.	class Admin extends User { }
super	Parent Class Access	Calls the parent class constructor or accesses its methods.	constructor(name) { super(name); }

Working with asynchronous results, Promise handlers, and async and await syntax.

Term / Syntax	Name	Description	Example
Promise	Asynchronous Result	Represents the eventual completion or failure of an asynchronous operation.	const promise = fetch(url);
.then()	Promise Fulfillment Handler	Runs a function when a Promise is fulfilled and returns a new Promise.	promise.then(value => console.log(value));
.catch()	Promise Rejection Handler	Runs a function when a Promise is rejected and returns a new Promise.	promise.catch(error => console.error(error));
.finally()	Promise Completion Handler	Runs a function when a Promise settles, whether it is fulfilled or rejected.	promise.finally(() => hideLoading());
Promise.all()	Wait for Multiple Promises	Waits for all provided Promises to fulfill and returns their values together, but rejects if any Promise rejects.	const results = await Promise.all([first, second]);
Promise.allSettled()	Wait for All Promise Results	Waits for all provided Promises to settle and returns the outcome of each one.	const results = await Promise.allSettled([first, second]);
async	Asynchronous Function	Declares a function that always returns a Promise and allows await inside it.	async function loadData() { }
await	Wait for Promise	Waits for a Promise to settle, returning its fulfilled value or throwing if it rejects.	const data = await loadData();

Sharing and loading values between JavaScript modules.

Term / Syntax	Name	Description	Example
export	Module Export	Makes values available to another module.	export function formatDate(date) { }
import	Module Import	Loads exported values from another module.	import { formatDate } from "./utils.js";

Creating, throwing, and handling errors when JavaScript operations fail.

Term / Syntax	Name	Description	Example
new Error()	Error Object	Creates an Error object with a message describing what went wrong.	const error = new Error("Invalid value");
try...catch	Error Handling	Runs code that may throw an error and handles the error if one occurs.	try { parseData(); } catch (error) { console.error(error); }
throw	Throw Error	Throws an error that can be handled by surrounding error-handling code.	throw new Error("Invalid value");