`js const name = "Alice"; const age = 30; // Old way const msg1 = "Hello, " + name + "! You are " + age + " years old."; // Template literal const msg2 = `Hello, ${name}! You are ${age} years old.`; // Expressions inside ${} const msg3 = `Next year you'll be ${age + 1}`; ``` ### Multi-line strings ```js // Old way (needed \n) const html1 = "

Hello

"; // Template literal (natural multi-line) const html2 = `

Hello

`; ``` ### Tagged templates ```js function highlight(strings, ...values) { return strings.reduce((result, str, i) => result + str + (values[i] ? `${values[i]}` : ""), ""); } const item = "apple"; const price = 1.5; const result = highlight`Item: ${item}, Price: $${price}`; // "Item: apple, Price: $1.5" ``` 27:T51f,## Question What is a Promise in JavaScript? ## Answer A **Promise** is an object representing the eventual completion or failure of an asynchronous operation. It has three states: - **Pending** – initial state - **Fulfilled** – operation completed successfully - **Rejected** – operation failed ```js const promise = new Promise((resolve, reject) => { const success = true; if (success) { resolve("Data fetched!"); } else { reject("Error occurred!"); } }); promise .then(data => console.log(data)) // "Data fetched!" .catch(err => console.error(err)) .finally(() => console.log("Done")); ``` ### Real-world example: fetch API ```js fetch("https://api.example.com/users") .then(response => response.json()) .then(data => console.log(data)) .catch(error => console.error(error)); ``` ### Promise combinators ```js // Wait for ALL to resolve Promise.all([fetch(url1), fetch(url2)]).then(([res1, res2]) => { }); // First one to settle wins Promise.race([fetch(url1), fetch(url2)]).then(result => { }); // Wait for ALL to settle (regardless of success/failure) Promise.allSettled([p1, p2]).then(results => { }); ``` ## Key Points - Promises solve "callback hell" - `async/await` is syntactic sugar over Promises - Always handle rejections with `.catch()` or `try/catch` 28:T542,## Question What is `async/await` in JavaScript? ## Answer `async/await` (ES2017) is syntactic sugar over Promises that makes asynchronous code look and behave like synchronous code. ### `async` function ```js async function fetchUser() { return "Alice"; // automatically wrapped in a resolved Promise } fetchUser().then(console.log); // "Alice" ``` ### `await` – pause until Promise resolves ```js async function getUser() { const response = await fetch("https://api.example.com/user/1"); const user = await response.json(); console.log(user.name); } ``` ### Error handling with `try/catch` ```js async function getData() { try { const response = await fetch("https://api.example.com/data"); if (!response.ok) throw new Error("Network error"); const data = await response.json(); return data; } catch (error) { console.error("Failed:", error.message); } } ``` ### Running in parallel ```js // Sequential (slow - waits for each) const user = await getUser(); const posts = await getPosts(); // Parallel (fast - both run at once) const [user, posts] = await Promise.all([getUser(), getPosts()]); ``` ## Key Points - `await` can only be used inside `async` functions - `async` functions always return a Promise - Use `try/catch` for error handling - Use `Promise.all` to run async operations in parallel 29:T485,## Question What are ES6 modules (`import`/`export`)? ## Answer ES6 modules let you split JavaScript code across multiple files and share functionality between them. ### Named exports ```js // math.js export const PI = 3.14159; export function add(a, b) { return a + b; } export function multiply(a, b) { return a * b; } ``` ```js // main.js import { PI, add } from "./math.js"; console.log(add(2, 3)); // 5 ``` ### Default export (one per file) ```js // greet.js export default function greet(name) { return `Hello, ${name}!`; } ``` ```js // main.js import greet from "./gree

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