JavaScript Quiz 3 Test your Knowledge on JavaScript

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What is the difference between == and === in JavaScript?

The double equals (==) operator compares values after converting them to a common type, while the triple equals (===) operator compares values without type conversion. This means that the triple equals operator is more strict than the double equals operator.

What is a closure in JavaScript?

A closure is a function that has access to variables in its outer (enclosing) function’s scope chain. This means that a closure can access variables defined in the outer function even after the outer function has returned.

What is the event loop in JavaScript?

The event loop is a mechanism in JavaScript that allows the runtime environment to continuously monitor the call stack and the message queue for new events. When the call stack is empty, the event loop takes the next event from the message queue and pushes it onto the call stack to be executed.

What is the difference between null and undefined in JavaScript?

Null is a value that represents the intentional absence of any object value, while undefined is a value that represents the absence of a defined value. In other words, null is a value that has been explicitly set to nothing, while undefined is a value that has not been defined or has been declared but not assigned a value.

What is hoisting in JavaScript?

Hoisting is a mechanism in JavaScript where variable and function declarations are moved to the top of their respective scopes, regardless of where they are actually declared in the code. This means that you can use a variable or function before it has been declared, as long as it is declared somewhere in the same scope.

What is the difference between var, let, and const in JavaScript?

Var is used to declare variables in JavaScript and has function scope, meaning it is accessible anywhere within the function in which it is declared. Let and const were introduced in ES6 and have block scope, meaning they are only accessible within the block in which they are declared. The main difference between let and const is that let variables can be reassigned, while const variables cannot be reassigned.

What is the difference between synchronous and asynchronous code in JavaScript?

Synchronous code is executed 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 call(), apply(), and bind() methods in JavaScript?

All three methods are used to set the value of this within a function, but they differ in how they accept arguments. Call() and apply() both immediately invoke the function with the provided this value and arguments (in the form of an array for apply()), while bind() returns a new function with the provided this value, but does not immediately invoke it.

What is the difference between destructuring and spreading in JavaScript?

Destructuring is a way to extract values from objects and arrays and assign them to variables, while spreading is a way to spread the values of an array or object into individual values. Destructuring is denoted by curly braces {} or square brackets [], while spreading is denoted by three dots (…).

What is the difference between a promise and an async/await function in JavaScript?

Both promises and async/await functions are used to handle asynchronous code in JavaScript, but they differ in syntax. Promises use a chain of .then() and .catch() methods to handle the eventual success or failure of an asynchronous operation, while async/await functions use the async keyword to mark a function as asynchronous, and the await keyword to wait for a promise to resolve