Skip to content

Master JavaScript interviews with our focused repository featuring essential questions, detailed answers, and practical examples. Elevate your preparation with expert insights and comprehensive coverage.

Notifications You must be signed in to change notification settings

w3flow/javascript-interview-questions-answers

Folders and files

NameName
Last commit message
Last commit date

Latest commit

 

History

62 Commits
 
 
 
 

Repository files navigation

Welcome to the JavaScript Interview Questions & Answers repository!

This repository is a comprehensive collection of JavaScript interview questions and answers designed to help you prepare for your next tech interview. Whether you're a beginner or an experienced developer, you'll find valuable insights and resources to sharpen your JavaScript skills and boost your confidence.

What's Inside

  • Detailed Q&A: In-depth questions and answers covering all aspects of JavaScript.
  • Concept Explanations: Clear explanations of fundamental and advanced JavaScript concepts.
  • Code Examples: Practical examples to help you understand and apply JavaScript concepts.
  • Interview Tips: Best practices and tips for acing your JavaScript interviews.

How to Use

  • Browse through the questions and answers to study and understand key JavaScript topics.
  • Use the code examples to practice and solidify your knowledge.
  • Follow the interview tips to improve your interview performance.

Contributing

We welcome contributions! If you have any JavaScript interview questions or answers that you'd like to share, please feel free to open an issue or submit a pull request.

Happy coding and good luck with your interviews!

Table of Contents

No. Title Show Answer
1 What is JavaScript?
Show Answer
2 Where can I use JavaScript?
Show Answer
3 Which libraries and frameworks are built in JavaScript?
Show Answer
4 What are primitive and non-primitive data types in JavaScript?
Show Answer
5 Understanding References in JavaScript
Show Answer
6 Including JavaScript Code in an HTML Document
Show Answer
7 What is the difference between let, var, and const?
Show Answer
8 How do you create a function in JavaScript?
Show Answer
9 What is a JavaScript object, and how do you create one?
Show Answer
10 What are arrays in JavaScript, and how do you use them?
Show Answer
11 How do you write comments in JavaScript?
Show Answer
12 What is the purpose of the this keyword in JavaScript?
Show Answer
13 What is the purpose of the this keyword in JavaScript?
Show Answer
14 What are JavaScript closures?
Show Answer
15 What are JavaScript promises?
Show Answer
16 What are the different types of loops in JavaScript?
Show Answer
17 How do you perform string concatenation in JavaScript?
Show Answer
18 What is the use of the typeof operator in JavaScript?
Show Answer
19 How do you create a multiline string in JavaScript?
Show Answer
20 What are JavaScript events, and how are they used?
Show Answer
21 How do you convert a string to a number in JavaScript?
Show Answer
22 What is the difference between null and undefined?
Show Answer
23 How do you use template literals in JavaScript?
Show Answer
24 What are JavaScript operators, and what types exist?
Show Answer
25 How do you write a conditional statement in JavaScript?
Show Answer
26 What is the difference between alert, prompt, and confirm in JavaScript?
Show Answer
27 How do you perform arithmetic operations in JavaScript?
Show Answer
28 How do you access and modify HTML elements using JavaScript?
Show Answer
29 What are primitive and reference types in JavaScript?
Show Answer
30 How do you use the instanceof operator in JavaScript?
Show Answer
31 What are default values for function parameters in JavaScript?
Show Answer
32 How do you format a date in JavaScript?
Show Answer
33 What is the eval function in JavaScript, and why is it considered dangerous?
Show Answer
34 How do you create a regular expression in JavaScript?
Show Answer
35 How do you use the parseInt and parseFloat functions in JavaScript?
Show Answer
36 How do you use the Date object to get the current date and time?
Show Answer
37 What is the purpose of the with statement in JavaScript, and why is it discouraged?
Show Answer
38 How do you check if a variable is an array in JavaScript?
Show Answer
39 What are the different ways to create an array in JavaScript?
Show Answer
40 How do you add and remove items from an array in JavaScript?
Show Answer
41 How do you change the content of an HTML element using JavaScript?
Show Answer
42 What is type coercion in JavaScript?
Show Answer
# Intermediate JavaScript Questions Answer
43 What is the this keyword, and how is its context determined?
Show Answer
44 How do you clone an object in JavaScript?
Show Answer
45 What are the different ways to iterate over an array in JavaScript?
Show Answer
46 How do you create and handle custom events in JavaScript?
Show Answer
47 What are arrow functions, and how do they differ from regular functions?
Show Answer
48 How do you debounce and throttle functions in JavaScript?
Show Answer
49 What is the purpose of the Object.freeze method?
Show Answer
50 How do you merge two or more objects in JavaScript?
Show Answer
51 What is the difference between method and function in JavaScript?
Show Answer
52 How do you use the Array.prototype.reduce method?
Show Answer
53 What is a higher-order function in JavaScript?
Show Answer
54 How do you create a private variable in JavaScript?
Show Answer
55 What is debouncing and throttling in JavaScript?
Show Answer
56 How do you use the fetch API to make HTTP requests?
Show Answer
57 What are generator functions in JavaScript, and how do they work?
Show Answer
58 How do you create a custom iterator in JavaScript?
Show Answer
59 How do you create a deep copy of an object in JavaScript?
Show Answer
60 What are rest parameters, and how are they used in JavaScript?
Show Answer
61 How do you implement method chaining in JavaScript?
Show Answer
62 How do you remove duplicates from an array in JavaScript?
Show Answer
63 What is the difference between for...of and for...in loops in JavaScript?
Show Answer
64 How do you handle cross-origin requests in JavaScript?
Show Answer
65 How do you use the Proxy object in JavaScript?
Show Answer
66 What is the Reflect object, and how is it used in JavaScript?
Show Answer
67 How do you debounce a function in JavaScript?
Show Answer
68 What is the window object in JavaScript, and what are its properties and methods?
Show Answer
# Advanced JavaScript Questions Answer
- ------------------------------------------------------------------------ ----------------------------------------
69 How do you use Proxy and Reflect in JavaScript?
Show Answer
70 What is the concept of "hoisting" in JavaScript?
Show Answer
71 What is a service worker in JavaScript?
Show Answer
72 How do you implement a web worker in JavaScript?
Show Answer
73 What are the benefits of using WebAssembly with JavaScript?
Show Answer
74 How do you create a singleton pattern in JavaScript?
Show Answer
75 What is memoization in JavaScript, and how do you implement it?
Show Answer
76 How do you perform deep cloning of objects in JavaScript?
Show Answer
77 What are the different ways to optimize memory usage in JavaScript?
Show Answer
78 How do you manage state in a JavaScript application?
Show Answer
79 What is the difference between mutable and immutable objects in JavaScript?
Show Answer
80 How do you use the Reflect API in JavaScript?
Show Answer
81 What is the module pattern in JavaScript?
Show Answer
82 How do you implement inheritance using ES6 classes?
Show Answer
83 What is a WeakMap in JavaScript, and how does it differ from a Map?
Show Answer
84 How do you handle circular references in JavaScript objects?
Show Answer
85 What is a microtask, and how does it differ from a macrotask in JavaScript?
Show Answer
86 How do you implement a binary search algorithm in JavaScript?
Show Answer
87 What are the benefits of using immutable data structures in JavaScript?
Show Answer
88 How do you implement lazy loading in JavaScript?
Show Answer
89 What are tagged templates in JavaScript?
Show Answer
90 How do you implement a debounce function in JavaScript?
Show Answer
91 How do you implement a simple pub/sub (publish-subscribe) system in JavaScript?
Show Answer
92 What is tail call optimization in JavaScript?
Show Answer
93 How do you create a memoization function in JavaScript?
Show Answer
94 What is the Blob object in JavaScript, and how is it used?
Show Answer
95 How do you work with binary data in JavaScript?
Show Answer
96 What is the File API in JavaScript, and how do you use it?
Show Answer
97 How do you handle large datasets efficiently in JavaScript?
Show Answer
98 How do you create and manage WebSockets in JavaScript?
Show Answer
99 What are the differences between localStorage, sessionStorage, and cookies in JavaScript?
Show Answer
100 How do you implement a state machine in JavaScript?
Show Answer
101 What is the DOM, and how is it structured?
Show Answer
102 How do you select an element by its ID using JavaScript?
Show Answer
103 How do you select elements by their class name using JavaScript?
Show Answer
104 How do you select elements by their tag name using JavaScript?
Show Answer
105 How do you create a new element and add it to the DOM?
Show Answer
106 How do you remove an element from the DOM?
Show Answer
107 How do you add an event listener to an element in the DOM?
Show Answer
108 What is the difference between innerHTML and textContent?
Show Answer
109 How do you change the style of an element using JavaScript?
Show Answer
110 How do you use the Array.prototype.filter method?
Show Answer
111 How do you use the Array.prototype.map method?
Show Answer
112 What is the purpose of the Array.prototype.some method?
Show Answer
113 How do you find the index of an element in an array using JavaScript?
Show Answer
114 How do you merge two arrays in JavaScript?
Show Answer
115 How do you convert an array to a string in JavaScript?
Show Answer
116 What is the Array.prototype.every method used for?
Show Answer
117 How do you find the first occurrence of a value in an array?
Show Answer
118 How do you sort an array of objects by a property?
Show Answer
119 How do you use the Array.prototype.slice method?
Show Answer
120 How do you find the length of a string in JavaScript?
Show Answer
121 How do you convert a string to uppercase in JavaScript?
Show Answer
122 How do you check if a string contains a specific substring?
Show Answer
123 How do you split a string into an array of substrings?
Show Answer
124 How do you replace a part of a string with another string?
Show Answer
125 How do you extract a substring from a string?
Show Answer
126 How do you trim whitespace from the beginning and end of a string?
Show Answer
127 How do you concatenate two strings in JavaScript?
Show Answer
128 How do you repeat a string a specified number of times?
Show Answer
129 How do you use template literals for string interpolation?
Show Answer
130 What is the BOM, and what objects does it include?
Show Answer
131 How do you get the width and height of the browser window?
Show Answer
132 How do you open a new browser window using JavaScript?
Show Answer
133 How do you navigate to a new URL using JavaScript?
Show Answer
134 How do you get the current URL of the browser window?
Show Answer
135 How do you interact with the browser history using JavaScript?
Show Answer
136 How do you set a timeout to execute a function after a delay?
Show Answer
137 How do you repeatedly execute a function at specified intervals?
Show Answer
138 How do you detect the user's browser and version using JavaScript?
Show Answer
139 How do you use the navigator object to get information about the user's environment?
Show Answer
140 How do you get and set an element's attributes using JavaScript?
Show Answer
141 How do you find all elements that match a specific CSS selector?
Show Answer
142 How do you clone a DOM element and its children?
Show Answer
143 How do you listen for changes to a form input field?
Show Answer
144 How do you get the value of a selected option in a dropdown?
Show Answer
145 How do you add a class to an element using JavaScript?
Show Answer
146 How do you remove a class from an element using JavaScript?
Show Answer
147 How do you toggle a class on an element using JavaScript?
Show Answer
148 How do you prevent the default action of an event?
Show Answer
149 How do you stop event propagation?
Show Answer
150 How do you use the Array.prototype.reduceRight method?
Show Answer
151 What is the Array.prototype.flat method, and how is it used?
Show Answer
152 How do you use the Array.prototype.flatMap method?
Show Answer
153 How do you use the Array.prototype.fill method to modify an array?
Show Answer
154 What is the Array.prototype.copyWithin method used for?
Show Answer
155 How do you create an array from an iterable or array-like object?
Show Answer
156 How do you use the Array.from method with a map function?
Show Answer
157 How do you use the Array.prototype.reverse method?
Show Answer
158 What is the Array.prototype.keys method, and how is it used?
Show Answer
159 How do you find the last index of an element in an array?
Show Answer
160 How do you use the String.prototype.startsWith method?
Show Answer
161 How do you use the String.prototype.endsWith method?
Show Answer
162 What is the String.prototype.includes method used for?
Show Answer
163 How do you use the String.prototype.charAt method?
Show Answer
164 How do you get the character code of a character in a string?
Show Answer
165 How do you convert a character code to a character?
Show Answer
166 What is the String.prototype.codePointAt method, and how is it used?
Show Answer
167 How do you normalize a string in JavaScript?
Show Answer
168 How do you pad a string to a certain length?
Show Answer
169 How do you match a string against a regular expression?
Show Answer
170 How do you use the location object to reload the current page?
Show Answer
171 How do you use the window object to move or resize the browser window?
Show Answer
172 How do you detect if cookies are enabled in the user's browser?
Show Answer
173 How do you get the user's screen dimensions using JavaScript?
Show Answer
174 How do you use the history.pushState method to modify the browser history?
Show Answer
175 How do you listen for changes in the browser history state?
Show Answer
176 How do you detect when the user goes online or offline?
Show Answer
177 How do you use the setTimeout function to delay the execution of code?
Show Answer
178 How do you clear a timeout or interval that you have set?
Show Answer
179 How do you use the alert, prompt, and confirm methods for user interaction?
Show Answer
180 What are async functions and how do you use them?
Show Answer
181 How do you use the async/await syntax in JavaScript?
Show Answer
182 What is the purpose of the try...catch statement in JavaScript?
Show Answer
183 How do you handle errors in asynchronous code in JavaScript?
Show Answer
184 What is callback hell, and how do you avoid it?
Show Answer
185 How do you use named exports in JavaScript modules?
Show Answer
186 How do you use default exports in JavaScript modules?
Show Answer
187 What are JavaScript modules, and how do you use them?
Show Answer
188 How do you import and export modules in JavaScript?
Show Answer
189 How do you implement inheritance in JavaScript using classes?
Show Answer
190 What are JavaScript decorators, and how do you use them?
Show Answer
191 What are generators in JavaScript, and how do they work?
Show Answer
192 How do you create iterators in JavaScript?
Show Answer
193 How do you use symbols in JavaScript?
Show Answer
194 What are Sets and how do you use them in JavaScript?
Show Answer
195 How do you use Promises in JavaScript?
Show Answer
196 How do you use async/await in JavaScript?
Show Answer
197 What is Event Delegation in JavaScript?
Show Answer
198 How do you handle Cross-Site Scripting (XSS) in JavaScript?
Show Answer
199 What is the JavaScript Event Loop?
Show Answer
200 How do you implement a callback function in JavaScript?
Show Answer
201 How do you handle symbol type in JavaScript? (ES6)
Show Answer
202 How do you use iterators and generators in JavaScript? (ES6)
Show Answer
203 How do you handle async iterators in JavaScript? (ES2018)
Show Answer
204 How do you handle big integer operations? (ES2020)
Show Answer
205 How do you use decorators in JavaScript? (Proposed)
Show Answer
206 How do you handle the optional catch binding proposal? (ES2019)
Show Answer
207 How do you use the globalThis proposal in JavaScript? (ES2020)
Show Answer
208 How do you use the nullish coalescing operator? (ES2020)
Show Answer
209 How do you use the optional chaining operator? (ES2020)
Show Answer
210 How do you handle error causes in JavaScript? (Proposed ES2023)
Show Answer
211 How do you use the class static block? (ES2022)
Show Answer
212 How do you handle top-level await in JavaScript? (ES2022)
Show Answer
213 How do you handle weak references in JavaScript? (ES2021)
Show Answer
214 How do you handle numeric separators in JavaScript? (ES2021)
Show Answer
215 How do you use the logical assignment operators? (ES2021)
Show Answer
216 How do you use Promise.allSettled method? (ES2020)
Show Answer
217 How do you implement functional programming concepts in JavaScript?
Show Answer
218 How do you use the pipeline operator proposal in JavaScript? (Proposed)
Show Answer
219 How do you use the throw expressions proposal in JavaScript? (Proposed)
Show Answer
220 How do you handle the record and tuple proposal? (Proposed ES2024)
Show Answer
221 How do you use the pattern matching proposal in JavaScript? (Proposed ES2024)
Show Answer
222 How do you implement the temporal API in JavaScript? (Proposed ES2024)
Show Answer
223 What are module attributes in JavaScript? (Proposed ES2024)
Show Answer
224 How do you implement a task scheduler in JavaScript?
Show Answer
225 How do you create a debounce function in JavaScript?
Show Answer
226 How do you create a throttle function in JavaScript?
Show Answer
227 How do you use setTimeout and setInterval in JavaScript?
Show Answer
228 How do you handle asynchronous iterations in JavaScript?
Show Answer
229 How do you use weak references and finalization registry? (ES2021)
Show Answer
230 How do you implement a priority queue in JavaScript?
Show Answer
231 How do you handle logical assignment operators? (ES2021)
Show Answer
232 How do you handle the numeric separators proposal? (ES2021)
Show Answer
233 How do you use iterators and generators? (ES6)
Show Answer
234 How do you implement a graph data structure in JavaScript?
Show Answer
235 How do you implement a binary search tree in JavaScript?
Show Answer
236 How do you implement a linked list in JavaScript?
Show Answer
237 How do you handle concurrency in JavaScript using web workers?
Show Answer
238 How do you use the Atomics and SharedArrayBuffer objects in JavaScript?
Show Answer
239 What are the new features in ES2024?
Show Answer
240 How do you use the pattern matching proposal in JavaScript? (Proposed ES2024)
Show Answer
241 How do you use record and tuple types in JavaScript? (Proposed ES2024)
Show Answer
242 How do you implement the temporal API in JavaScript? (Proposed ES2024)
Show Answer
243 What are module attributes in JavaScript? (Proposed ES2024)
Show Answer

1. What is JavaScript?

JavaScript is a versatile, high-level programming language primarily used for adding interactivity to web pages. It operates as an interpreted language, executing code line by line without prior compilation.

Historical Context

JavaScript was created by Brendan Eich in 1995 while he was at Netscape Communications Corporation. Originally named "Mocha" and later "LiveScript," it was rebranded as JavaScript to align with the popularity of Java.

Key Features

  • Dynamic Typing: Variables can hold values of any data type without explicit declarations.

  • Prototype-based Object Orientation: Objects inherit properties and behaviors from prototypes.

  • Functional Programming Support: Functions are treated as first-class citizens, enabling higher-order functions and closures.

Move to Top


2. Where can I use JavaScript?

JavaScript can be used for both client-side and server-side development. It's integral to creating interactive web pages, developing web and mobile applications, building APIs, and even for server-side programming using platforms like Node.js.

Move to Top


3. Which libraries and frameworks are built in JavaScript?

JavaScript has a rich ecosystem of libraries and frameworks that simplify and enhance development. Some popular examples include:

  • React.js: A JavaScript library for building user interfaces.

  • AngularJS and Angular: Frameworks for building web applications.

  • Node.js: A runtime environment that allows JavaScript to run server-side.

These tools and frameworks extend JavaScript's capabilities beyond basic scripting, enabling robust application development across various platforms.

Move to Top


4. What are primitive and non-primitive data types in JavaScript?

JavaScript supports different data types, categorized into primitive and non-primitive types.

  • Primitive data: Primitive data types in JavaScript are immutable (unchangeable) and are directly operated upon by the language. They are stored directly in the variable's memory and are accessed by value.
Data Type Description Example
number Represents numeric data. let count = 10;
string Represents textual data. let message = 'Hello';
boolean Represents logical values. let isValid = true;
null Represents intentional absence of any object value. let data = null;
undefined Represents a variable declared but not assigned a value. let status;
symbol Represents a unique identifier. const id = Symbol('unique');
  • Non-primitive: Non-primitive data types are mutable (changeable) and are not stored directly in the variable's allocated memory. Instead, they are stored as references, and accessing these variables points to the reference in memory.
Data Type Description Example
object Represents a collection of key-value pairs. let person = { name: 'John', age: 30 };
array Represents a list-like collection of elements. let numbers = [1, 2, 3, 4, 5];
function Represents a reusable block of code. function greet(name) { return 'Hello, ' + name; }

Move to Top


5. Understanding References in JavaScript.

In JavaScript, references play a crucial role in how non-primitive data types are managed in memory. Unlike primitive data types (like numbers and strings) that are stored directly in the variable's location, non-primitive types (such as objects, arrays, and functions) are stored as references.

How References Work

When you create a non-primitive data type, what actually gets stored in the variable is a reference to the memory location where the data is stored, rather than the data itself. This means:

  1. Reference to Memory: Variables holding non-primitive types don't contain the actual data values but rather pointers or references to where the data resides in memory.

  2. Passing by Reference: When you assign a non-primitive variable to another variable or pass it as an argument to a function, you're passing around this reference. This allows multiple variables to point to the same underlying data structure.

  3. Mutability: Non-primitive types are mutable because you can change their properties or elements through their references. Modifying an object's property or adding/removing elements from an array affects the referenced data directly.

Benefits of Reference-Based Storage

  • Memory Efficiency: References enable efficient memory usage because you're not duplicating large data structures every time you assign or pass them.

  • Flexibility: Referencing allows for complex data structures and dynamic changes without heavy memory overhead. This flexibility is crucial in modern JavaScript applications, where objects and arrays are commonly used to represent complex data relationships.

Example

// Example of referencing in JavaScript

// Object creation let person1 = { name: 'John', age: 30 };

// person2 references the same object as person1 let person2 = person1;

// Modifying person2 affects the referenced object person2.age = 35;

console.log(person1.age); // Output: 35 (because person1 and person2 point to the same object)

Move to Top


6. Including JavaScript Code in an HTML Document?

To include JavaScript code in an HTML document, you can use the <script> tag. Here's how it works:

Script Tag

Use the <script> tag within the <head> or <body> section of your HTML document.

Inline JavaScript

You can write JavaScript code directly within <script> tags in your HTML file:

<script> // Your JavaScript code here alert('Hello, World!'); </script>

Inline JavaScript

Alternatively, you can link to an external JavaScript file using the src attribute of the <script> tag.

<script src="path/to/your/script.js"></script>

Move to Top

7. What is the difference between let, var, and const?

In JavaScript, let, var, and const are used to declare variables, but they behave differently in terms of scoping, hoisting, and mutability. Understanding their differences is crucial for writing clean and maintainable code.

var

In JavaScript, variables can be declared using var. Understanding how var behaves in terms of scoping, hoisting, and mutability is important for writing robust and maintainable code.

  • Scope: var variables are function-scoped or globally-scoped. They are not block-scoped, which means they are visible throughout the entire function or global context.
  • Hoisting: Variables declared with var are hoisted to the top of their function or global scope. This means you can use the variable before it's declared in the code.
  • Reassignable: var variables can be redeclared and reassigned within their scope.

Example:

function example() {
  var x = 10;
  if (true) {
    var x = 20;
    console.log(x); // Outputs: 20
  }
  console.log(x); // Outputs: 20
}

let

In JavaScript, let is used to declare variables that are block-scoped. This means they are limited to the block ({ }) in which they are defined, such as if, for, or while blocks.

  • Scope: let variables are block-scoped, meaning they are limited to the block ({ }) in which they are defined, such as if, for, or while blocks.
  • Hoisting: Variables declared with let are hoisted to the top of their block, but unlike var, they are not initialized until their declaration is evaluated. Accessing a let variable before its declaration results in a ReferenceError.
  • Reassignable: let variables can be reassigned but cannot be redeclared in the same scope.

Example:

function example() {
  let x = 10; // Declaring 'x' using let
  if (true) {
    let x = 20; // 'x' redeclared within the block
    console.log(x); // Outputs: 20
  }
  console.log(x); // Outputs: 10 (outside the block)
}

example();

const

In JavaScript, const is used to declare variables that are block-scoped and must be initialized with a value that cannot be reassigned.

  • Scope: const variables are block-scoped, meaning they are limited to the block ({ }) in which they are defined, such as if, for, or while blocks.
  • Hoisting: Variables declared with const are hoisted to the top of their block, but they are not initialized until their declaration is evaluated.
  • Immutability: const variables must be initialized with a value when declared, and once initialized, their value cannot be reassigned. However, for objects and arrays, properties can be mutated.

Example:

function example() {
  const x = 10; // Declaring 'x' using const
  // x = 20; // Error: Assignment to constant variable 'x' is not allowed
  const y = { name: 'John' }; // Declaring 'y' as a const object
  y.name = 'Jane'; // Valid: Changing property of a const object
  console.log(y); // Outputs: { name: 'Jane' }
}

example();

Choosing Between let, var, and const

When working with variables in JavaScript, choosing between let, var, and const depends on their intended usage and requirements:

  • Use const by default: Use const for variables that will not be reassigned. This promotes immutability and helps prevent accidental reassignments.

  • Use let for variables that need to be reassigned: When you anticipate that a variable's value will change during the program's execution, opt for let. This approach provides clarity and avoids confusion about the variable's mutability.

  • Avoid var unless necessary: var has broader scope rules and can lead to unexpected behaviors due to hoisting and lack of block scoping. However, in some legacy code or specific scenarios where you need function-scoped variables, var may still be used.

Understanding the differences between let, var, and const will enable you to choose the appropriate variable declaration based on your specific programming needs and best practices. Move to Top

8. How do you create a function in JavaScript?

Functions in JavaScript are essential for organizing and reusing code. There are several methods to create functions, each suited for different scenarios and coding styles.

1. Function Declaration (Named function declaration)

Function declarations are defined using the function keyword, followed by the function name, parameters (optional), and a function body enclosed in curly braces {}.

Example:

// Function declaration
function greet(name) {
  return `Hello, ${name}!`;
}

// Calling the function
console.log(greet("Alice")); // Outputs: Hello, Alice!

2. Function Expression (anonymous function)

Function expressions define functions using the function keyword without specifying a function name (anonymous function). These can be assigned to variables or passed as arguments to other functions.

Example:

// Function expression (anonymous function)
const greet = function(name) {
  return `Hello, ${name}!`;
};

// Calling the function
console.log(greet("Bob")); // Outputs: Hello, Bob!

3. Arrow Function (ES6+)

Arrow functions provide a concise syntax introduced in ES6. They use the => syntax and automatically bind this to the surrounding context.

Example:

// Arrow function
const greet = (name) => {
  return `Hello, ${name}!`;
};

// Calling the function
console.log(greet("Eve")); // Outputs: Hello, Eve!

4. Method Functions (Object method function)

In JavaScript, functions can also be defined as methods within objects or classes. These functions are associated with specific objects and are invoked using dot notation (object.method())

Example:

// Method function
const person = {
  name: "John",
  greet: function() {
    return `Hello, ${this.name}!`;
  }
};

// Calling the method function
console.log(person.greet()); // Outputs: Hello, John!

Move to Top

9. What is a JavaScript object, and how do you create one?

In JavaScript, an object is a fundamental data structure consisting of key-value pairs. It allows you to store and access data through named properties. Objects are versatile and can represent complex data structures.

Creating an Object

There are several ways to create objects in JavaScript:

1. Object Literal Syntax

let person = {
    firstName: 'John',
    lastName: 'Doe',
    age: 30,
    hobbies: ['reading', 'music', 'sports'],
    address: {
        street: '123 Main St',
        city: 'Anytown',
        state: 'CA'
    },
    fullName: function() {
        return this.firstName + ' ' + this.lastName;
    }
};

2. Using the new Keyword with Object Constructor.

let person = new Object();
person.firstName = 'John';
person.lastName = 'Doe';
person.age = 30;
person.hobbies = ['reading', 'music', 'sports'];
person.address = {
    street: '123 Main St',
    city: 'Anytown',
    state: 'CA'
};
person.fullName = function() {
    return this.firstName + ' ' + this.lastName;
};

3. Using Object.create() Method.

let personPrototype = {
    fullName: function() {
        return this.firstName + ' ' + this.lastName;
    }
};

let person = Object.create(personPrototype);
person.firstName = 'John';
person.lastName = 'Doe';
person.age = 30;
person.hobbies = ['reading', 'music', 'sports'];
person.address = {
    street: '123 Main St',
    city: 'Anytown',
    state: 'CA'
};

4. Using ES6 Classes.

class Person {
    constructor(firstName, lastName, age) {
        this.firstName = firstName;
        this.lastName = lastName;
        this.age = age;
    }

    fullName() {
        return `${this.firstName} ${this.lastName}`;
    }
}

let person = new Person('John', 'Doe', 30);

Accessing Object Properties

You can access properties of an object using dot notation (.) or bracket notation ([]):

console.log(person.firstName); // Outputs: John
console.log(person['lastName']); // Outputs: Doe

Modifying Object Properties

You can modify properties of an object after its creation:

person.age = 32;
person['hobbies'].push('painting');

Object Methods

Objects can contain functions as values. These functions are called methods:

let person = {
    firstName: 'John',
    lastName: 'Doe',
    fullName: function() {
        return this.firstName + ' ' + this.lastName;
    }
};

console.log(person.fullName()); // Outputs: John Doe

Move to Top

10. What are arrays in JavaScript, and how do you use them?

In JavaScript, an array is a special type of object used to store multiple values in a single variable. Arrays allow you to group values of any data type (including other arrays) sequentially under a single identifier. They are versatile and commonly used for storing lists of items or collections of related data.

Creating Arrays

There are several ways to create arrays in JavaScript:

1. Array Literal Syntax.

let fruits = ['Apple', 'Banana', 'Cherry', 'Date'];

2. Using the new Keyword with Array Constructor.

let fruits = new Array('Apple', 'Banana', 'Cherry', 'Date');

However, using array literal syntax ([]) is generally preferred due to its simplicity and readability.

  • Accessing Array Elements: You can access elements in an array using square brackets ([]) and the index of the element (0-based index):
let fruits = ['Apple', 'Banana', 'Cherry', 'Date'];

console.log(fruits[0]); // Outputs: Apple
console.log(fruits[2]); // Outputs: Cherry
  • Modifying Array Elements: You can modify elements in an array directly by assigning a new value to a specific index:
let fruits = ['Apple', 'Banana', 'Cherry', 'Date'];

fruits[1] = 'Orange';
console.log(fruits); // Outputs: ['Apple', 'Orange', 'Cherry', 'Date']
  • Array Properties and Methods Arrays in JavaScript have various properties and methods that allow you to manipulate them effectively:
  • Length Property : Returns the number of elements in the array.
console.log(fruits.length); // Outputs: 4

  • Push Method : Adds one or more elements to the end of an array and returns the new length of the array.
fruits.push('Fig');
console.log(fruits); // Outputs: ['Apple', 'Orange', 'Cherry', 'Date', 'Fig']

Move to Top

11. How do you write comments in JavaScript?

In JavaScript, comments are used to annotate code and provide explanations or notes that are ignored by the JavaScript engine during execution. They are helpful for documenting code, explaining functionality, and making it easier for other developers (or your future self) to understand.

Types of Comments

JavaScript supports two main types of comments:

1. Single-Line Comments:

Single-line comments start with // and continue until the end of the line. They are used for brief comments on a single line of code.

// This is a single-line comment
let greeting = 'Hello'; // This comment explains the variable purpose

2. Multi-Line Comments:

Multi-line comments start with /* and end with */. They can span across multiple lines and are typically used for longer explanations or commenting out multiple lines of code.

/*
 * This is a multi-line comment.
 * It can span across several lines.
 * These comments are often used for detailed explanations or notes.
 */

let message = 'Welcome'; /* This comment is inline with code */

Move to Top

About

Master JavaScript interviews with our focused repository featuring essential questions, detailed answers, and practical examples. Elevate your preparation with expert insights and comprehensive coverage.

Topics

Resources

Stars

Watchers

Forks

Releases

No releases published

Packages

No packages published