JavaScript Challenges: Preparing for Your Web Development Interview

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FAQ

What is the purpose of hoisting in JavaScript?

Hoisting is JavaScript’s default behavior of moving declarations to the top of the current scope (to the top of the current script or the current function). This means that variables and function declarations are processed before any code is executed, allowing them to be used before they are declared.

How do you create a private variable in JavaScript?

To create a private variable in JavaScript, you can use closures. A closure is an inner function that has access to the variables in the outer (enclosing) function’s scope chain. By defining variables within the enclosing function, you can make them private to the outside scope, accessible only through methods defined in the same closure.

Can you explain the difference between “==” and “===” operators in JavaScript?

Yes, “==” is the equality operator that checks for equality of value but not equality of type. It converts both values to a common type before comparing. On the other hand, “===” is the strict equality operator that checks for equality of both value and type, meaning no type conversion is performed.

What are promises in JavaScript and how do they work?

Promises in JavaScript represent the eventual completion (or failure) of an asynchronous operation and its resulting value. A promise is an object that may produce a single value in the future: either a resolved value or a reason that it’s not resolved (e.g., a network error occurred). It allows you to associate handlers with an asynchronous action’s eventual success value or failure reason.

Describe what a callback function is and provide a use case.

A callback function is a function passed into another function as an argument, which is then invoked inside the outer function to complete some kind of routine or action. A common use case is making asynchronous calls, such as web API requests, where the callback function is executed once the request completes to handle the response.

How does event bubbling work in the DOM?

Event bubbling is a method of event propagation in the DOM where events start from the innermost element that triggered the event (the target), then propagate up through the series of ancestors in the hierarchy. This means that when an event is fired on an element that is nested within another element, the inner element’s event is handled first and then the outer element’s event is handled.

What is the purpose of the ‘this’ keyword in JavaScript?

The ‘this’ keyword in JavaScript refers to the object it belongs to. It has different values depending on where it is used: in a method, ‘this’ refers to the owner object; alone, ‘this’ refers to the global object; in a function, ‘this’ refers to the global object in non-strict mode and undefined in strict mode; in an event, ‘this’ refers to the element that received the event.

Explain how inheritance works in JavaScript.

In JavaScript, inheritance works through the prototype chain. Every object has a private property (prototype) which holds a link to another object called its prototype. That prototype object has its own prototype, and so on until an object with a null prototype is reached. Properties and methods are inherited in a chain from the prototype, allowing objects to inherit features from one another.

What is the use of the ‘forEach’ method in JavaScript?

The ‘forEach’ method in JavaScript is used to execute a provided function once for each array element. It is a part of Array’s prototype and provides an easy way to iterate over arrays without using a traditional for loop, allowing you to execute a function on each element of the array.

How can you avoid callback hell in JavaScript?

You can avoid callback hell by using Promises, async/await, or libraries that simplify asynchronous operations. Promises provide a cleaner and more manageable way to handle asynchronous operations by chaining .then() for successive operations or catching errors. Async/await makes it even simpler to work with promises, allowing asynchronous code to be written in a synchronous-like manner, making it easier to read and understand.
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