JavaScript Quiz with Answers
What is the difference between == and === operators in JavaScript?
What is the difference between null and undefined in JavaScript?
What is the difference between let and var in JavaScript?
What is a closure in JavaScript?
What is the difference between call() and apply() in JavaScript?
What is a promise in JavaScript?
What is event bubbling in JavaScript?
What is a higher-order function in JavaScript?
What is the difference between synchronous and asynchronous code in JavaScript?
What is the difference between a cookie and a session in JavaScript?
What is the difference between == and === operators in JavaScript?
The == operator compares the values of two variables without checking their data types, while the === operator compares both the values and the data types of two variables. For example, 1 == ‘1’ would return true, whereas 1 === ‘1’ would return false.
What is the difference between null and undefined in JavaScript?
In JavaScript, null is a value that represents the intentional absence of any object value, while undefined is a variable that has been declared but has not yet been assigned a value. In other words, null is a value that has been intentionally set to signify an empty or non-existent state, whereas undefined occurs when a variable has not been initialized.
What is the difference between let and var in JavaScript?
In JavaScript, let and var are both used to declare variables. However, the main difference between the two is that let is block-scoped, meaning it is only accessible within the block it is defined in, while var is function-scoped, meaning it is accessible throughout the entire function it is defined in.
What is a closure in JavaScript?
A closure is a feature in JavaScript that allows a function to access variables outside of its own scope, even after the function has returned. This is accomplished by creating a function within a function, and returning the inner function as a value. The inner function is then able to access the variables in the outer function’s scope, even after the outer function has finished executing.
What is the difference between call() and apply() in JavaScript?
Both call() and apply() are methods in JavaScript that allow you to call a function with a specified this value and arguments. However, the main difference between the two is the way in which you pass arguments to the function. With call(), you pass arguments directly as a comma-separated list, while with apply(), you pass arguments as an array.
What is a promise in JavaScript?
A promise is an object in JavaScript that represents the eventual completion (or failure) of an asynchronous operation, and allows you to chain together multiple asynchronous operations in a more readable way. Promises have three states: pending (the initial state), fulfilled (meaning the operation completed successfully), and rejected (meaning the operation failed).
What is event bubbling in JavaScript?
Event bubbling is a process in JavaScript where when an event is triggered on an element, the event will “bubble up” through the DOM tree, triggering any parent elements that have the same event listener. This can lead to unintended behavior if you’re not careful, as events can be triggered multiple times.
What is a higher-order function in JavaScript?
A higher-order function is a function that takes another function as an argument, or returns a function as a value. This allows for more flexibility and modularity in your code, as you can pass in different functions as arguments to achieve different results.
What is the difference between synchronous and asynchronous code in JavaScript?
Synchronous code is code that executes in a single, sequential order, blocking other code from executing until it is complete. Asynchronous code, on the other hand, does not block other code from executing, and can run simultaneously with other code. This is useful for handling long-running operations that would otherwise freeze up your application.
What is the difference between a cookie and a session in JavaScript?
Both cookies and sessions are ways of storing data on the client side in JavaScript. Cookies are small text files that are stored on the user’s computer and are sent to the server with each subsequent request. Sessions, on the other hand, store data on the server side and are maintained between requests. This makes sessions more secure than cookies, as the user cannot modify them directly.