Prompt Title: 100 JS Q&A with Answers

Sure! Here are 100 more JavaScript questions along with their answers:

1. What is the purpose of JavaScript? Answer: JavaScript is a scripting language used to add interactivity and dynamic content to web pages. It allows developers to create interactive web applications and enhance user experience.

2. What is the difference between == and === in JavaScript? Answer: == is used for loose equality comparison, and === is used for strict equality comparison. With ===, both the value and the type of the operands must be the same for the comparison to be true, while == performs type coercion before making the comparison.

3. How do you check if a variable is an array in JavaScript? Answer: You can use the Array.isArray() method to check if a variable is an array:

   javascriptCopy code
   const arr = [1, 2, 3];
   console.log(Array.isArray(arr)); // Output: true
   

4. What is the difference between null and undefined? Answer: null is a value that represents the intentional absence of any object value, while undefined is a type and value that represents an uninitialized or undefined variable.

5. Explain the concept of hoisting in JavaScript. Answer: Hoisting is a JavaScript behavior where variable and function declarations are moved to the top of their containing scope during the compilation phase. However, only declarations are hoisted, not the initializations. For example:

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   console.log(x); // Output: undefined
   var x = 5;
   

6. What is the DOM (Document Object Model)? Answer: The DOM is a programming interface for HTML and XML documents. It represents the structure of the document as a tree of nodes, where each node corresponds to an element, attribute, or text within the document. JavaScript can manipulate the DOM to modify the content and structure of web pages dynamically.

7. Explain the purpose of the use strict directive in JavaScript. Answer: The 'use strict'; directive is used to enable strict mode in JavaScript, which enforces a stricter set of rules for writing code. It helps to avoid common pitfalls and improves the overall code quality.

8. What are closures in JavaScript, and how are they used? Answer: Closures are functions that have access to variables from their outer (enclosing) function, even after the outer function has finished executing. This allows for data encapsulation and the creation of private variables in JavaScript.

9. How do you handle asynchronous operations in JavaScript? Answer: Asynchronous operations in JavaScript are commonly handled using callbacks, promises, or async/await. Callbacks are functions that are passed as arguments and executed when the asynchronous task is completed. Promises and async/await are modern approaches that provide more structured and readable ways to handle asynchronous code.

10. What is the purpose of the bind() method in JavaScript? Answer: The bind() method is used to create a new function with a specific this context, which is set explicitly. It is often used to bind a function to a particular object, ensuring that the this keyword behaves as expected when the function is called.

11. How do you create an object in JavaScript? Answer: There are multiple ways to create objects in JavaScript. One common approach is using object literal notation:

    javascriptCopy code
    const person = {
      name: "John",
      age: 30,
      sayHello: function() {
        console.log("Hello!");
      },
    };
    

12. What is the this keyword in JavaScript? Answer: The this keyword in JavaScript refers to the context within which a function is called. It represents the object on which the current method or function is being invoked. The value of this depends on how a function is called (e.g., as a method, with call or apply, etc.).

13. What are the different data types in JavaScript? Answer: JavaScript has the following primitive data types: number, string, boolean, null, undefined, and symbol. Additionally, it has a complex data type called object that includes arrays, functions, and objects.

14. What is the difference between let, const, and var in JavaScript? Answer: let and const are block-scoped, meaning they are limited in scope to the block (e.g., within curly braces) where they are defined. var, on the other hand, is function-scoped and can lead to some unexpected behaviors. const variables cannot be reassigned after declaration, while let variables can be.

15. What are the default methods of the Array object in JavaScript? Answer: Some of the default methods of the Array object in JavaScript are push(), pop(), shift(), unshift(), slice(), splice(), concat(), join(), indexOf(), lastIndexOf(), forEach(), map(), filter(), reduce(), and sort().

16. What is event bubbling in JavaScript? Answer: Event bubbling is a phenomenon in which an event triggered on a specific element propagates up through its parent elements in the DOM hierarchy. If an event handler is registered on both the specific element and its parent, both handlers will be executed.

17. How do you check if a given variable is a function in JavaScript? Answer: You can use the typeof operator to check if a variable is a function:

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    function greet() {
      console.log("Hello!");
    }
    console.log(typeof greet === "function"); // Output: true
    

18. Explain the concept of prototypal inheritance in JavaScript. Answer: In JavaScript, objects can inherit properties and methods from other objects through their prototype chain. When a property or method is accessed on an object, if it doesn't exist on the object itself, JavaScript looks for it in the object's prototype, and this process continues up the chain until the property or method is found or the top of the chain (Object.prototype) is reached.

19. What is the difference between let and var? Answer: Both let and var are used for variable declaration, but let is block-scoped, whereas var is function-scoped. Variables declared with var are hoisted to the top of their scope, while let variables are not hoisted.

20. How do you compare two objects for equality in JavaScript? Answer: In JavaScript, two objects are considered equal only if they refer to the same memory location. There is no built-in method for deep object comparison. However, libraries like Lodash provide utility functions for deep object comparison.

21. What is the purpose of the window object in JavaScript? Answer: In the browser environment, the window object represents the global scope and serves as the top-level object for accessing various properties