What is JavaScript? JavaScript is a high-level, dynamic, and interpreted programming language that is commonly used to add interactivity and dynamic effects to web pages.
What are the key features of JavaScript? JavaScript is a lightweight, interpreted, and dynamically typed language that supports a variety of programming paradigms including procedural, functional, and object-oriented programming. It supports event-driven programming and is often used for client-side scripting in web development.
What is the difference between JavaScript and Java? JavaScript and Java are two distinct programming languages with different syntax and features. While JavaScript is primarily used for client-side scripting on the web, Java is a general-purpose programming language used for developing a wide range of applications.
What are the data types in JavaScript? JavaScript supports six primitive data types: string, number, boolean, undefined, null, and symbol. It also supports object and function data types.
What is NaN in JavaScript? NaN stands for “Not a Number” and is a value returned when a mathematical operation or function cannot produce a meaningful result.
What is the difference between null and undefined in JavaScript? In JavaScript, null represents an intentional absence of any object value, while undefined represents a variable that has been declared but has not been assigned a value.
What is hoisting in JavaScript? Hoisting is a JavaScript behavior where variable and function declarations are moved to the top of their respective scopes during the compilation phase. This means that a variable or function can be used before it is declared.
What is closure in JavaScript? A closure is a function that has access to variables in its outer scope, even after the outer function has returned. This allows for a powerful and flexible programming paradigm that supports things like private variables and encapsulation.
What is the difference between synchronous and asynchronous code execution in JavaScript? Synchronous code executes in a blocking manner, meaning that the program waits for each operation to complete before moving on to the next one. Asynchronous code, on the other hand, executes non-blocking, meaning that the program can continue to run while waiting for a particular operation to complete.
What is callback in JavaScript? A callback is a function that is passed as an argument to another function and is executed when a certain condition is met or when an operation is complete.
What is a promise in JavaScript? A promise is a built-in object in JavaScript that represents the eventual completion or failure of an asynchronous operation and provides a way to handle the result once it is available.
What is the difference between let and var in JavaScript? The let keyword is used to declare block-scoped variables, while the var keyword is used to declare function-scoped variables. In addition, variables declared with let are not hoisted, meaning they cannot be used before they are declared.
What is the difference between == and === in JavaScript? The == operator compares values for equality after converting both operands to a common type, while the === operator compares values for strict equality, meaning that both the value and the type must be the same.
What is event bubbling in JavaScript? Event bubbling is a JavaScript behavior where an event that is triggered on an inner element is propagated up the DOM tree to its parent elements.
What is the difference between call and apply methods in JavaScript? Both the call and apply methods are used to invoke a function with a specific context, but the call method accepts arguments as a comma-separated list, while the apply method accepts arguments as an array.
What is the difference between let and const in JavaScript? The let keyword is used to declare block-scoped variables that can be reassigned, while the const keyword is used to declare block-scoped variables that cannot be reassigned once they have been initialized.
What is a higher-order function in JavaScript? A higher-order function is a function that takes one or more functions as arguments or returns a function as its result.
What is the difference between a for loop and a forEach loop in JavaScript? A for loop is a traditional loop construct that allows you to iterate over a range of values and perform a certain action on each iteration. A forEach loop is a method available on arrays that allows you to iterate over each element in the array and perform a certain action on each element.
What is the spread operator in JavaScript? The spread operator (…) is a new feature in JavaScript that allows you to expand an array or object into individual elements or properties.
What is destructuring in JavaScript? Destructuring is a feature in JavaScript that allows you to extract values from arrays or objects and assign them to variables in a more concise way.
What is the difference between a closure and a module in JavaScript? A closure is a function that has access to variables in its outer scope, while a module is a self-contained block of code that encapsulates its variables and functions to provide a certain functionality.
What is the difference between synchronous and asynchronous code execution in JavaScript? Synchronous code executes in a blocking manner, meaning that the program waits for each operation to complete before moving on to the next one. Asynchronous code, on the other hand, executes non-blocking, meaning that the program can continue to run while waiting for a particular operation to complete.
What is the difference between a class and an object in JavaScript? A class is a blueprint for creating objects, while an object is an instance of a class.
What is the difference between a method and a function in JavaScript? A method is a function that is a property of an object, while a function is a stand-alone block of code that can be called from anywhere in the program.
What is a prototype in JavaScript? A prototype is an object that is associated with every function and object in JavaScript and is used to provide inheritance and to share properties and methods between objects.
What is a promise in JavaScript? A promise is an object that represents a value that may not be available yet but will be resolved at some point in the future, either successfully or unsuccessfully.
What is async/await in JavaScript? Async/await is a syntax for working with promises that allows you to write asynchronous code in a more synchronous style.
What is the difference between let and var in JavaScript? The let keyword is used to declare block-scoped variables that can be reassigned, while the var keyword is used to declare function-scoped variables that can be reassigned.
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 value.
What is hoisting in JavaScript? Hoisting is a behavior in JavaScript where variable and function declarations are moved to the top of their respective scopes before code execution.
What is a callback function in JavaScript? A callback function is a function that is passed as an argument to another function and is executed when the other function has completed its task.
What is a closure in JavaScript? A closure is a function that has access to variables in its outer scope, even after the outer function has returned.
What is event bubbling in JavaScript? Event bubbling is a mechanism in JavaScript where events that are triggered on a nested element are propagated up the DOM tree to the parent elements.
What is the difference between innerHTML and textContent in JavaScript? InnerHTML is a property that allows you to set or retrieve the HTML content of an element, while textContent is a property that allows you to set or retrieve the text content of an element.