certified coder Interview Questions and Answers

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100 Certified Coder Interview Questions and Answers

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

    • Answer: `==` performs loose equality comparison, checking only for value equality after type coercion. `===` performs strict equality comparison, checking for both value and type equality without coercion. For example, `1 == "1"` is true, but `1 === "1"` is false.

  2. Explain the concept of hoisting in JavaScript.

    • Answer: Hoisting is a JavaScript mechanism where declarations of variables and functions are moved to the top of their scope before code execution. This means you can use a variable or function before its declaration in the code, but only if it's declared (not just assigned a value) later in the scope. However, note that only the *declaration* is hoisted, not the *initialization*.

  3. What are closures in JavaScript?

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

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

    • Answer: `var` is function-scoped (or globally scoped if not inside a function). `let` and `const` are block-scoped. `const` declares a constant value, which cannot be reassigned after its initial declaration. `let` allows reassignment.

  5. Explain the concept of prototypal inheritance in JavaScript.

    • Answer: JavaScript uses prototypal inheritance. Every object has a prototype (another object) from which it inherits properties and methods. When you try to access a property on an object, JavaScript first searches the object itself. If it's not found, it searches the prototype, and then the prototype's prototype, and so on, until it reaches the end of the prototype chain (usually `null`).

  6. What is AJAX and how does it work?

    • Answer: AJAX (Asynchronous JavaScript and XML) is a technique for updating parts of a web page without reloading the whole page. It works by using JavaScript to make asynchronous requests to a server. The response from the server is then used to update the page dynamically.

  7. Explain the concept of event bubbling in JavaScript.

    • Answer: Event bubbling is the order in which events are handled in the DOM tree. When an event occurs on an element, it is first handled by that element. If the event is not handled, it "bubbles up" to the parent element, and then to its parent, and so on, until it reaches the root element (document).

  8. What are promises in JavaScript?

    • Answer: Promises are a way to handle asynchronous operations in JavaScript. A promise represents the eventual result of an asynchronous operation. It can be in one of three states: pending, fulfilled (resolved), or rejected.

  9. What is async/await and how does it work?

    • Answer: Async/await is a syntactic sugar for working with promises. `async` declares an asynchronous function that implicitly returns a promise. `await` pauses execution of an async function until a promise resolves (or rejects).

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