computer language coder Interview Questions and Answers

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100 Interview Questions and Answers for Computer Language Coders

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

    • Answer: == performs loose equality comparison, while === performs strict equality comparison. Loose equality coerces types before comparison (e.g., "1" == 1 is true), while strict equality checks both value and type (e.g., "1" === 1 is false).

  2. Explain the concept of closures in JavaScript.

    • Answer: A closure is a function that has access to variables from its surrounding scope, even after that scope has finished executing. This allows functions to "remember" their environment.

  3. What are the different ways to declare a variable in JavaScript?

    • Answer: var (function-scoped), let (block-scoped), and const (block-scoped, for constants).

  4. What is the difference between synchronous and asynchronous programming?

    • Answer: Synchronous code executes line by line. Asynchronous code allows other tasks to execute while waiting for a long-running operation (like a network request) to complete, often using callbacks, promises, or async/await.

  5. Explain the concept of "this" keyword in JavaScript.

    • Answer: The this keyword refers to the object that is executing the current function. Its value depends on how the function is called (e.g., directly, as a method of an object, or using call() or apply()).

  6. What is a Promise in JavaScript?

    • Answer: A Promise is an object representing the eventual completion (or failure) of an asynchronous operation and its resulting value. It can be in one of three states: pending, fulfilled, or rejected.

  7. What is event delegation in JavaScript?

    • Answer: Event delegation involves attaching an event listener to a parent element instead of individual child elements. When an event occurs on a child element, the event bubbles up to the parent, triggering the listener. This is more efficient than attaching listeners to many elements.

  8. Explain how prototypal inheritance works in JavaScript.

    • Answer: JavaScript uses prototypal inheritance. Every object has a prototype, which is another object it inherits properties and methods from. This creates a prototype chain.

  9. What are some common design patterns in JavaScript?

    • Answer: Examples include Module, Singleton, Factory, Observer, MVC (Model-View-Controller).

  10. What is the difference between null and undefined in JavaScript?

    • Answer: null is an assignment value representing the intentional absence of a value. undefined means a variable has been declared but hasn't been assigned a value.

  11. Explain how to handle errors in JavaScript.

    • Answer: Use try...catch blocks to handle exceptions. try contains the code that might throw an error, and catch handles the error.

  12. What are some best practices for writing clean and maintainable JavaScript code?

    • Answer: Use consistent indentation, meaningful variable names, comments, modularity (breaking code into smaller reusable functions), and linters/formatters.

  13. What is AJAX and how does it work?

    • Answer: AJAX (Asynchronous JavaScript and XML) allows web pages to update asynchronously by exchanging data with a server, without reloading the entire page. It typically uses XMLHttpRequest or the Fetch API.

  14. Explain the concept of JSON (JavaScript Object Notation).

    • Answer: JSON is a lightweight data-interchange format. It's easy for humans to read and write, and easy for machines to parse and generate.

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