Synchronous vs asynchronous execution in Javascript - Quick Revision & Key Differences

Recall & Review

beginner

What does synchronous execution mean in JavaScript?

Synchronous execution means the code runs line by line, one after another. Each step waits for the previous one to finish before starting.

beginner

What is asynchronous execution in JavaScript?

Asynchronous execution lets some code run in the background, so the program can keep doing other things without waiting for that code to finish.

intermediate

Which JavaScript feature allows asynchronous code to run without blocking the main thread?

Promises and async/await allow asynchronous code to run without blocking the main thread, so the program stays responsive.

beginner

Give an example of a synchronous operation.

A simple math calculation like adding two numbers is synchronous because it happens immediately and the next line waits for it to finish.

beginner

Why is asynchronous execution important in web development?

It keeps the website responsive by not freezing the page while waiting for things like data from the internet or timers.

What happens in synchronous JavaScript execution?

A Code runs one line at a time, waiting for each to finish

B Code runs multiple lines at the same time

C Code runs only after a timer

D Code runs only when user clicks

Synchronous execution means each line waits for the previous one to finish before running.

Which of these is an example of asynchronous JavaScript?

A A for loop adding numbers

B Fetching data from a server

C Declaring a variable

D Simple math calculation

Fetching data from a server happens asynchronously so the program doesn't freeze while waiting.

What JavaScript feature helps handle asynchronous code easily?

A Functions

B Variables

C Loops

D Promises

Promises help manage asynchronous operations by allowing code to run after a task finishes.

Why might synchronous code cause problems in a web page?

A It uses too little memory

B It runs too fast

C It can freeze the page while waiting

D It never finishes

Synchronous code can block the page, making it unresponsive until the task finishes.

Which keyword is used to write asynchronous functions in JavaScript?

A async

B sync

C wait

D defer

The 'async' keyword marks a function as asynchronous, allowing use of 'await' inside it.

Explain the difference between synchronous and asynchronous execution in JavaScript.

Think about how the program waits or doesn't wait for tasks to finish.

Why is asynchronous execution useful for web pages and user experience?

Consider what happens if the page waits for a slow task.