practiceSheetEndTerm.md

Practice Sheet: Asynchronous Programming in JavaScript

Part 1: Conceptual Questions

1. What is asynchronous programming, and why is it important in JavaScript?
2. Explain the difference between synchronous and asynchronous code execution.
3. What is a callback function? Provide an example.
4. What are some of the common problems associated with using callbacks extensively?
5. What is a Promise in JavaScript? How does it improve code readability over callbacks?
6. Explain the different states of a Promise and what they represent.
7. How does the .then() method work with Promises?
8. What is the purpose of the .catch() method in Promises?
9. How does async/await simplify working with Promises?
10. Can async/await be used without Promises? Why or why not?

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Part 2: Coding Exercises

1. Write a function fetchData(callback) that simulates fetching data from an API. Use setTimeout to delay the execution for 2 seconds. The function should return either data or an error message via the callback.

2. Convert the following callback-based function into one that uses Promises:

   function getUserData(callback) {
       setTimeout(() => {
           callback(null, { name: "John", age: 25 });
       }, 1000);
   }

3. Write a Promise-based function getTemperature(city) that resolves with a simulated temperature for the given city after 2 seconds.

4. Given the following code snippet, fix it using .catch() to handle the error:

   fetchWeatherData()
       .then(data => console.log(data))
       .then(() => console.log("Done"));

5. Use async/await to refactor the following code:

   function fetchUser() {
       return new Promise(resolve => {
           setTimeout(() => resolve({ name: "Alice" }), 1000);
       });
   }
   fetchUser().then(user => console.log(user));

6. Create an async function that fetches user data and weather data sequentially using the following mock functions:

   function getUser() {
       return new Promise(resolve => setTimeout(() => resolve("User data"), 1000));
   }
   function getWeather() {
       return new Promise(resolve => setTimeout(() => resolve("Weather data"), 1000));
   }

7. Handle multiple Promises using Promise.all to fetch details of three users simultaneously.

8. Rewrite the following code to handle errors gracefully using try...catch:

   async function fetchUserData() {
       let response = await fetch("/user");
       let data = await response.json();
       console.log(data);
   }

9. Write an async function that throws an error intentionally and handles it using try...catch.

10. Create a chain of Promises that simulates a series of dependent asynchronous operations:

    • Fetch user profile
    • Fetch user settings based on profile
    • Fetch recommendations based on settings

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Part 3: Debugging and Logical Thinking

1. What happens if you forget to use await inside an async function? Provide an example.

2. Identify the issue with the following code and correct it:

   async function fetchData() {
       setTimeout(() => {
           return "Data";
       }, 1000);
   }
   let data = fetchData();
   console.log(data);

3. Why does the following code result in a rejected Promise, and how can you fix it?

   function fetchItems() {
       return new Promise((resolve, reject) => {
           setTimeout(() => reject("Error fetching items"), 2000);
       });
   }
   fetchItems().then(items => console.log(items));

4. Rewrite the following function to use Promise.allSettled:

   const promise1 = Promise.resolve("Data 1");
   const promise2 = Promise.reject("Error in Data 2");
   const promise3 = Promise.resolve("Data 3");
   Promise.all([promise1, promise2, promise3]).then(results => console.log(results));

5. Consider the following code. Will it work as intended? Explain why or why not:

   async function processData() {
       const data = fetch("/data");
       console.log(await data.json());
   }
   processData();

6. Write an async function that demonstrates the usage of Promise.race with two Promises: one that resolves quickly and another that takes longer.

7. What is the difference between Promise.all and Promise.race? Provide an example for each.

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Challenge Question

1. Create a small program that simulates a "Retry Mechanism" using Promises. The function should attempt to fetch data from a mocked API up to 3 times if it encounters an error.

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