1. What is JavaScript and what are its key features?
JavaScript is a high-level, interpreted programming language primarily used for web development. Its key features include being event-driven, prototype-based, dynamically typed, and having first-class functions. It supports functional, object-oriented, and imperative programming styles.
2. What are the differences between JavaScript and Java?
JavaScript is an interpreted language, primarily used for web development to create interactive effects within web browsers. Java, on the other hand, is a compiled, statically-typed programming language used for building applications that run on the Java Virtual Machine (JVM). JavaScript is dynamically typed, whereas Java requires explicit declaration of variable types.
3. Explain the difference between let, var, and const in JavaScript.
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var is function-scoped and can be redeclared and updated.-
let is block-scoped and can be updated but not redeclared within the same scope.-
const is block-scoped and cannot be updated or redeclared, but the properties of objects declared with const can be modified.4. What is a closure in JavaScript?
A closure is a function that retains access to its lexical scope, even when the function is executed outside that scope. This allows the function to access variables from its defining scope even after that scope has finished executing.
5. How do you handle asynchronous operations in JavaScript?
Asynchronous operations in JavaScript can be handled using callbacks, Promises, or async/await. Callbacks are functions passed as arguments to other functions, Promises represent eventual completion or failure of an asynchronous operation, and async/await allows writing asynchronous code that looks synchronous.
6. What is the Document Object Model (DOM) and how do you manipulate it using JavaScript?
The DOM is a programming interface for HTML and XML documents, representing the structure of a document as a tree of objects. JavaScript can manipulate the DOM using methods like
getElementById(), querySelector(), createElement(), and properties like innerHTML and style.7. Explain the difference between == and === in JavaScript.
The
== operator performs type coercion, meaning it converts the operands to the same type before comparing them. The === operator, on the other hand, does not perform type coercion and compares both value and type directly.8. What is the event loop in JavaScript?
The event loop is a mechanism that allows JavaScript to perform non-blocking, asynchronous operations. It continuously checks the call stack and the message queue. If the call stack is empty, it takes the first event from the message queue and pushes it to the call stack, allowing asynchronous callbacks to be executed.
9. How do you create and use a JavaScript module?
JavaScript modules can be created using the
export keyword to export functions, objects, or primitives from a file, and the import keyword to import them into another file. This promotes modular code and reuse of functionality across different parts of an application.10. How do you handle errors in JavaScript?
Errors in JavaScript can be handled using
try-catch blocks. The code that may throw an error is placed in the try block, and any exceptions are caught and handled in the catch block. Additionally, a finally block can be used to execute code regardless of whether an exception occurs.You can check these resources for Coding interview Preparation
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