coding tech Interview Questions and Answers

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100 Coding Interview Questions and Answers

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

    • Answer: `==` performs loose equality comparison, meaning it coerces the operands to the same type before comparison. `===` performs strict equality comparison, meaning it only returns true if the operands are of the same type and have the same value. For example, `1 == "1"` is true, but `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(s), even after that scope has finished executing. This allows inner functions to "remember" and use variables from their outer functions, even after the outer functions have returned.

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

    • Answer: `null` is an assignment value that represents the intentional absence of a value. `undefined` means a variable has been declared but has not been assigned a value. `typeof null` returns "object" (a historical quirk), while `typeof undefined` returns "undefined".

  4. What is event bubbling in JavaScript?

    • Answer: Event bubbling is the order in which events propagate through the DOM tree. When an event occurs on an element, it first triggers the event handler on that element. Then, the event "bubbles up" the DOM tree, triggering event handlers on its parent elements until it reaches the root element (document).

  5. How do you prevent default behavior in JavaScript?

    • Answer: You can prevent the default behavior of an event using the `preventDefault()` method. For example, in a form submission event, `event.preventDefault()` would prevent the form from submitting in the usual way.

  6. Explain the concept of hoisting in JavaScript.

    • Answer: Hoisting is a JavaScript mechanism where variables and function declarations are moved to the top of their scope before code execution. However, only the declarations are hoisted, not the assignments. This means variables will have the value `undefined` before their declaration line is reached, while function declarations are fully hoisted and can be called before their declaration.

  7. What is prototypal inheritance in JavaScript?

    • Answer: Prototypal inheritance is a mechanism where objects inherit properties and methods from other objects. Every object in JavaScript has a prototype, which is another object it inherits from. This creates a prototype chain, allowing objects to inherit properties and methods from their prototypes and their prototypes' prototypes, and so on.

  8. What are promises in JavaScript?

    • Answer: Promises are objects that represent the eventual result of an asynchronous operation. They can be in one of three states: pending, fulfilled, or rejected. They provide a cleaner way to handle asynchronous operations compared to callbacks, avoiding "callback hell".

  9. Explain async/await in JavaScript.

    • Answer: `async/await` is a syntactic sugar built on top of promises. `async` makes a function return a promise, and `await` pauses execution until a promise resolves (or rejects).

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