Advanced Javascript Interview Questions
Master the Art of Advanced JavaScript: Expert Interview Questions and Answers
Advanced JavaScript interview questions are designed to test the candidate's knowledge and understanding of advanced JavaScript concepts and techniques. These questions require more in-depth understanding of JavaScript, including its core principles, functional programming, asynchronous programming, DOM manipulation, error handling, and debugging. They are used by employers to assess a candidate's practical skills and problem-solving abilities, as well as their ability to write efficient, clean, and scalable code. In addition to technical knowledge, these questions may also gauge the candidate's familiarity with popular JavaScript libraries and frameworks, and their ability to adapt to new technologies and stay updated in the fast-paced world of web development. Adequate preparation and practice are essential to excel in advanced JavaScript interviews.
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1 - What is JavaScript?
JavaScript is a high level, interpreted programming language that is used for creating dynamic and interactive websites. It was initially created as a client side scripting language, but now it is also used for server side development. It is commonly used alongside HTML and CSS to add functionality to web pages.
2) What is the difference between let, var, and const in JavaScript?
Let, var, and const are all used for declaring variables in JavaScript. The main difference between them is their scope and hoisting behavior. Var variables are function scoped, meaning they are accessible within the entire function they are declared in. Let and const variables are block scoped, meaning they are available only within the block they are declared in. Var variables are also hoisted, meaning they can be used before they are declared, while let and const variables are not hoisted.
3) What is the event loop in JavaScript?
The event loop is a mechanism in JavaScript that handles asynchronous functions. Whenever a task is executed, it is added to a task queue. The event loop constantly checks the task queue and executes the tasks one by one, only after the execution of the previous task is completed. This allows JavaScript to handle multiple tasks without blocking the main thread, making it possible to create responsive and interactive web applications.
4) What is a closure in JavaScript?
A closure is an inner function that has access to variables and parameters of its outer (enclosing) function. It allows the inner function to access and modify variables declared in the outer function, even after the outer function has returned. This helps in creating private variables and data encapsulation in JavaScript.
5) What is the difference between an explicit and implicit type conversion in JavaScript?
Explicit type conversion, also known as type casting, is done explicitly by the programmer using built in methods or functions to convert one data type to another. Implicit type conversion, also known as type coercion, happens automatically by the JavaScript engine when an operation between two different data types is performed. For example, when a number is concatenated with a string, the number is implicitly converted to a string.
6) What is the difference between == and === in JavaScript?
The == operator checks for equality of values, whereas the === operator also checks for the equality of data types. This means that the == operator can convert the data types of operands, while the === operator cannot. For example, 1 == “1” would return true since the string “1” is converted to a number before comparison, but 1 === “1” would return false since the type of the operands is not the same.
7) What is a promise in JavaScript?
A promise is an object that represents the eventual completion or failure of an asynchronous operation. It allows us to write asynchronous code that can be handled in a similar way as synchronous code, making it easier to manage complex operations. A promise can have three states: pending, fulfilled, or rejected.
8) How does prototypal inheritance work in JavaScript?
Prototypal inheritance is a way of creating objects in JavaScript by linking them to a parent object. Every object in JavaScript has a prototype property which refers to the object from which it inherits its properties. If an object does not have a property, it will look for it in its prototype chain until it reaches the top level object, which is the base Object in JavaScript.
9) What is the difference between a let and const variables in terms of reassignment?
Let variables can be reassigned to a different value, while const variables cannot be reassigned. However, this rule only applies to reassignment of the entire variable, since const variables declared with complex data types, such as objects and arrays, can be modified. Its value cannot be completely reassigned to a different complex data type.
10) What is a higher order function in JavaScript?
A higher order function is a function that takes another function as an argument, or returns a function as its result. This allows us to write more flexible and reusable code, as we can pass different functions as arguments to the higher order function and get different results based on the logic of the passed function.
11) What is the difference between a for and for in loop in JavaScript?
A for loop is a traditional loop used for iterating over a given number of elements, while a for in loop is used for iterating over the properties of an object. A for loop can be used for both arrays and objects, but a for in loop should only be used for objects.
12) What is a NaN in JavaScript?
NaN stands for Not a Number and it is a specific value in JavaScript that represents an invalid number. It is returned when a mathematical operation cannot be performed due to incorrect data types, such as trying to perform mathematical operations on strings or undefined variables.
13) How does event bubbling work in JavaScript?
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Event bubbling is a mechanism in which an event is first handled at the most specific element and then it bubbles up to the parent elements. For example, if a button is clicked, the event will first be handled by the button and then it will bubble up to its parent elements, such as the form, body, and document.
14) What are the different data types in JavaScript?
JavaScript has seven primitive data types: string, number, boolean, null, undefined, symbol, and bigint. It also has one non primitive data type, which is object. Primitive data types are immutable, while objects can have their properties and values modified.
15) How does hoisting work in JavaScript?
Hoisting is a behavior in JavaScript in which all variable and function declarations are moved to the top of their scope. This means that variables and functions can be used before they are declared. However, only the declaration is hoisted, not the initialization, which means that the value will be undefined until it is assigned. This behavior only applies to variables declared with var, not let or const.
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