Preparing for a Technical Interview: Common Questions in JavaScript

Introduction

When preparing for a technical interview, it is important to be familiar with common questions that may be asked. In this article, we will discuss some common questions related to JavaScript and provide answers to help you prepare.

What is closure in JavaScript?

Closure in JavaScript is a combination of a function and the lexical environment within which that function was declared. It allows the function to remember the surrounding scope and access external variables. For example, a closure can be used to create private variables in JavaScript.

What is the difference between undefined and null in JavaScript?

Undefined is a value that indicates a variable has been declared but has not been assigned a value. Null, on the other hand, is a value that represents an empty or non-existent value explicitly assigned by a programmer.

What is a callback function in JavaScript and how is it used?

A callback function is a function that is passed into another function as an argument. It can be used to perform some action after a certain event or to pass business logic into the upper function. Callback functions are commonly used in asynchronous programming.

What

is the ES6 directive 'use strict' and how is it used?

The ‘use strict’ directive is used to enable strict mode in JavaScript. It makes JavaScript more strict by default in modules and prevents global declarations of variables, reassigning variables, and invoking ’this’ in arrow functions. It is recommended to use the ‘use strict’ directive as it helps catch common coding mistakes and leads to more robust code.

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

The double equal (==) operator compares values after performing type coercion, while the triple equal (===) operator compares both value and type. The triple equal operator is more strict and is generally recommended for equality comparisons in JavaScript.

What is hoisting in JavaScript?

Hoisting is a behavior in JavaScript where variable and function declarations are moved to the top of their containing scope during the compilation phase. Variables declared with ‘var’ are hoisted and can be accessed before they are declared, although they will have an initial value of undefined. Hoisting does not occur with variables declared with ’let’ or ‘const’.

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

Const, let, and var are all used to declare variables in JavaScript, but they have different scoping rules. Variables declared with const are block-scoped and cannot be reassigned after their initial assignment. Variables declared with let are also block-scoped but can be reassigned. Variables declared with var are function-scoped and can be reassigned.

What are some common data types in JavaScript?

Some common data types in JavaScript include string, number, undefined, object, symbol, and boolean. Understanding these data types is essential for working with JavaScript.

What are some common array methods in JavaScript?

JavaScript provides several built-in array methods that can be used to manipulate arrays. Some common array methods include forEach, map, filter, reduce, and every. These methods can be used to perform various operations on arrays and are essential for working with data.

What is a higher-order function in JavaScript?

A higher-order function is a function that takes in another function as an argument or returns a function as a result. Higher-order functions are commonly used in JavaScript, especially with array methods, to provide flexibility and enable code reuse.

Conclusion

Preparing for a technical interview can be challenging, but familiarizing yourself with common questions and their answers can greatly improve your chances of success. In this article, we discussed some common questions related to JavaScript and provided answers to help you prepare. Remember to practice and review these concepts to build your confidence and ace your technical interview.

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