Top 150+ JavaScript Interview Questions and Answers for full-stack Web Developer

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Prepare for your full-stack web developer JavaScript interview Questions and Answer From basic concepts to advanced topics, with our comprehensive JavaScript Interview Questions and Answers guide. Master essential concepts and ace your next technical interview.

JavaScript interview Questions and Answer for full-stack Web Developer

Dive into our friendly JavaScript Interview Questions and Answers guide in Full-Stack Web Development, chapter by chapter, designed for full-stack web developers like you! which is base on ECMA Script-262. Whether you’re brushing up on basics or exploring advanced topics, we’ve got you covered with simple explanations and helpful insights to ace your next interview with confidence. Another only Core JavaScript interviews questions & Answers you can prepare it.

Core JavaScript Concepts interview Questions:

1. What is JavaScript?
   • JavaScript is a high-level, interpreted programming language used to create interactive effects within web browsers.
2. What are the data types in JavaScript?
   • JavaScript has six primitive data types: string, number, boolean, null, undefined, and symbol. Additionally, there is an object data type.
3. Explain hoisting in JavaScript.
   • Hoisting is a JavaScript mechanism where variables and function declarations are moved to the top of their containing scope during the compile phase.
4. What is the difference between undefined and null?
   • undefined represents a variable that has been declared but has not been assigned a value, while null is an assignment value representing no value.
5. What is the this keyword in JavaScript?
   • The this keyword refers to the object to which the current code belongs. Its value depends on how a function is called.
6. What is the difference between == and ===?
   • == is used for equality comparison, where JavaScript performs type coercion if operands are of different types. === is used for strict equality comparison, where types and values must be the same.
7. Explain closures in JavaScript.
   • A closure is the combination of a function bundled together with references to its surrounding state. It gives you access to an outer function’s scope from an inner function.
8. What is event delegation in JavaScript?
   • Event delegation is a technique for listening to events where you delegate the responsibility of handling events to a common ancestor instead of handling the events on individual elements.
9. What is the event loop in JavaScript?
   • The event loop is a single-threaded mechanism that handles asynchronous callbacks in JavaScript. It continuously checks the call stack and the task queue, pushing tasks from the queue onto the stack when the stack is empty.
10. Explain the difference between let, const, and var.
    • var is function-scoped, let and const are block-scoped. var can be redeclared and reassigned, let can be reassigned but not redeclared, and const cannot be reassigned or redeclared.
11. What is the difference between dot notation and bracket notation?
    • Dot notation is used to access properties of an object using the dot (.) operator.
    • Bracket notation is used to access properties using square brackets ([]), and it allows for dynamic property names.
12. Explain object destructuring in JavaScript.
    • Object destructuring allows you to extract multiple properties from an object into separate variables.

interview Questions for JavaScript ES6+ Features:

11. What are arrow functions in JavaScript?
    • Arrow functions are a concise way to write anonymous function expressions in JavaScript, with a more intuitive syntax and lexical scoping of this.
12. What is a callback function?
    • A callback function is a function passed as an argument to another function, which is then invoked inside the outer function.
13. Explain destructuring in JavaScript.
    • Destructuring allows you to extract values from arrays or properties from objects into distinct variables.
14. What are template literals in JavaScript?
    • Template literals are string literals that allow embedded expressions, providing an easier way to concatenate strings and interpolate variables.
15. What is the ... spread operator in JavaScript?
    • The spread operator allows an iterable to be expanded in places where multiple arguments (for function calls) or multiple elements (for array literals) are expected.
16. What are the Map and Set data structures in JavaScript?
    • Map is a collection of key-value pairs, and Set is a collection of unique values.
17. Explain async/await in JavaScript.
    • async/await is a syntactic sugar for writing asynchronous code. It allows you to write asynchronous code in a synchronous manner, making it easier to read and maintain.
18. What are Promises in JavaScript?
    • Promises are objects representing the eventual completion or failure of an asynchronous operation. They are used to handle asynchronous computations.
19. What is the for...of loop in JavaScript?
    • The for...of loop is used to iterate over iterable objects such as arrays, strings, maps, sets, etc.
20. Explain the Object.entries() and Object.fromEntries() methods.
    • Object.entries() returns an array of a given object’s own enumerable string-keyed property [key, value] pairs. Object.fromEntries() transforms a list of key-value pairs into an object.
21. What is the Symbol data type in JavaScript?
    • Symbol is a primitive data type introduced in ECMAScript 6, used to create unique identifiers for object properties.
22. Explain the this keyword in JavaScript?
    • this refers to the object to which a function belongs or is called upon.
23. Explain the difference between function declaration and function expression.
    • Function declarations are hoisted, meaning they can be called before they’re defined.
    • Function expressions are not hoisted and cannot be called before they’re defined.

interview Questions for JavaScript DOM Manipulation:

21. What is the Document Object Model (DOM)?
    • The DOM is a programming interface for web documents. It represents the page so that programs can change the document structure, style, and content.
22. Explain how you would add an event listener in JavaScript.
    • You can use the addEventListener() method to attach an event handler to an element.
23. What is the difference between innerText and innerHTML?
    • innerText sets or returns the text content of the specified node, while innerHTML sets or returns the HTML content of an element.
24. How can you create elements dynamically in JavaScript?
    • You can use the document.createElement() method to create a new element, and then append it to an existing element using methods like appendChild().
25. Explain event bubbling and event capturing.
    • Event bubbling is the process where the event is first captured and handled by the innermost element and then propagated to outer elements. Event capturing is the opposite; the event is first captured by the outermost element and propagated to the inner elements.
26. What is the difference between window.onload and document.ready?
    • window.onload fires when the entire page (including images and external resources) is loaded, while document.ready (used in jQuery) fires when the DOM is ready, which may be before images are fully loaded.
27. How can you remove an element from the DOM?
    • You can use the removeChild() method to remove a child node from an element.
28. What is event delegation, and how does it work?
    • Event delegation is a technique for handling events where you attach a single event listener to a parent element instead of individual child elements. When an event occurs, it bubbles up to the parent, and you can determine which child element triggered the event.
29. What are data attributes, and how are they used?
    • Data attributes allow you to store extra information on HTML elements in the form of custom attributes prefixed with data-. They are commonly used to store data for JavaScript to access.
30. How can you get and set attributes of an HTML element in JavaScript?
    • You can use methods like getAttribute() and setAttribute() to get and set attributes of an HTML element.
31. How do you access elements in the DOM using JavaScript?
    • Using methods like getElementById(), getElementsByClassName(), getElementsByTagName(), querySelector(), and querySelectorAll().
32. How do you manipulate HTML content using JavaScript?
    • By accessing element properties such as innerHTML, textContent, innerText, value, etc.
33. How do you add and remove event listeners in JavaScript?
    • Using the addEventListener() method to add listeners and the removeEventListener() method to remove them.
34. Explain event propagation in JavaScript.
    • Event propagation refers to the order in which event handlers are executed when an event occurs on a DOM element.

interview Questions for Asynchronous JavaScript:

31. What is asynchronous programming in JavaScript?
    • Asynchronous programming is a programming paradigm that allows the CPU to perform other tasks while waiting for long-running tasks (such as I/O operations) to complete.
32. Explain callbacks in JavaScript.
    • A callback is a function passed as an argument to another function, which will be invoked or executed later.
33. What is the callback hell? How can you avoid it?
    • Callback hell refers to the situation where multiple nested callbacks make the code difficult to read and maintain. You can avoid it by using promises, async/await, or modularizing your code.
34. What are promises in JavaScript?
    • Promises are objects representing the eventual completion or failure of an asynchronous operation. They allow you to handle asynchronous computations in a more manageable way.
35. Explain the fetch API in JavaScript.
    • The fetch API is a modern replacement for XMLHttpRequest for making HTTP requests. It provides a more flexible and powerful interface for fetching resources from the network.
36. What are async functions in JavaScript?
    • Async functions are a syntactic sugar for writing asynchronous code using promises. They allow you to write asynchronous code in a synchronous manner, making it easier to read and maintain.
37. What is the purpose of the await keyword in JavaScript?
    • The await keyword is used to pause the execution of an async function until a promise is settled (resolved or rejected), and to resume execution after the promise is settled, with the resolved value returned by the promise.
38. How can you handle errors in asynchronous code in JavaScript?
    • You can use try...catch blocks or .catch() method chaining to handle errors in asynchronous code.
39. Explain the difference between Promise.all() and Promise.race().
    • Promise.all() takes an array of promises and returns a single promise that resolves when all of the input promises have resolved. Promise.race() takes an array of promises and returns a single promise that resolves or rejects as soon as one of the input promises resolves or rejects.
40. What are generators in JavaScript?
    • Generators are functions that can be paused and resumed. They allow you to generate a sequence of values lazily, on-demand.

interview Questions for JavaScript Modules:

45. What are modules in JavaScript?
    • Modules are reusable pieces of code that encapsulate related functionality.
46. How do you create and export modules in JavaScript?
    • Using the export keyword to export functions, variables, or objects from a module.
47. How do you import modules in JavaScript?
    • Using the import keyword to import functions, variables, or objects from a module.
48. What are named exports and default exports?
    • Named exports allow you to export multiple values from a module, while default exports allow you to export a single value.

interview Questions for Object-Oriented Programming (OOP) in JavaScript:

41. What is object-oriented programming (OOP)?
    • Object-oriented programming is a programming paradigm based on the concept of “objects,” which can contain data in the form of fields (properties) and code in the form of procedures (methods).
42. How can you create objects in JavaScript?
    • You can create objects using object literals, constructor functions, or the class syntax introduced in ES6.
43. Explain the concept of prototypes in JavaScript.
    • Prototypes are the mechanism by which JavaScript objects inherit features from one another. Each object has a prototype object from which it inherits properties and methods.
44. What is inheritance in JavaScript?
    • Inheritance is a mechanism by which an object can inherit properties and methods from another object. It allows for code reuse and promotes modularity.
45. What are constructor functions in JavaScript?
    • Constructor functions are functions used to create objects with a specific structure and behavior. They are typically used with the new keyword to create new instances of objects.
46. What is the prototype property in JavaScript?
    • The prototype property allows you to add properties and methods to an object’s prototype, which are then inherited by all instances of that object.
47. How do you create prototypes in JavaScript?
    • By adding properties and methods to the prototype object of a constructor function.
48. What is prototype chaining in JavaScript?
    • Prototype chaining is the process of searching for properties and methods in an object’s prototype chain if they are not found in the object itself.
49. Explain prototypal inheritance in JavaScript.
    • Prototypal inheritance is the ability of objects to inherit properties and methods from other objects.
50. What is the class keyword in JavaScript?
    • The class keyword is a syntactic sugar for defining constructor functions and prototype methods in a more concise and readable way.
51. Explain the super keyword in JavaScript.
    • The super keyword is used to call methods on an object’s parent class. It is used within constructor functions and methods of child classes to call corresponding methods or constructors of the parent class.
52. What is method chaining in JavaScript?
    • Method chaining is a technique where multiple methods are called on the same object in a single statement, with each method returning the object itself, allowing for the creation of fluent interfaces.
53. What is encapsulation in JavaScript?
    • Encapsulation is the bundling of data and methods that operate on the data into a single unit (object). It allows for the hiding of implementation details and the exposure of a controlled interface to the outside world.
54. What are constructors in JavaScript?
    • Constructors are special methods used for initializing objects created with a class.

interview Questions for Functional Programming in JavaScript:

51. What is functional programming?
    • Functional programming is a programming paradigm that treats computation as the evaluation of mathematical functions and avoids changing state and mutable data.
52. Explain pure functions in JavaScript.
    • A pure function is a function that always returns the same result given the same input and does not have any side effects. It does not modify variables outside its scope or change the state of the program.
53. What are higher-order functions in JavaScript?
    • Higher-order functions are functions that can take other functions as arguments or return functions as their result. They are a fundamental concept in functional programming.
54. What is currying in JavaScript?
    • Currying is the process of transforming a function that takes multiple arguments into a sequence of functions that each take a single argument. It allows for partial application of functions.
55. What is immutability in JavaScript?
    • Immutability is the concept of not changing the state of an object after it has been created. In JavaScript, immutable data structures are often used to ensure that data remains unchanged.
56. What is function composition in JavaScript?
    • Function composition is the process of combining two or more functions to produce a new function. It involves passing the output of one function as the input to another function.
57. Explain the map, filter, and reduce functions in JavaScript.
    • map is used to transform each element of an array using a given function. filter is used to create a new array with elements that pass a certain condition. reduce is used to reduce an array to a single value by applying a function to each element.
58. What are side effects in JavaScript?
    • Side effects are changes made to the state of a program that are observable outside the function performing the computation. They can include modifying external variables, performing I/O operations, or throwing exceptions.
59. What is memoization in JavaScript?
    • Memoization is an optimization technique used to speed up function calls by caching the results of expensive function calls and returning the cached result when the same inputs occur again.
60. What is recursion in JavaScript?
    • Recursion is a programming technique where a function calls itself in order to solve smaller instances of the same problem. It is often used in situations where a problem can be divided into smaller subproblems.

interview Questions for JavaScript Error Handling and Debugging:

61. How can you debug JavaScript code?
    • You can use browser developer tools, console.log statements, breakpoints, and debugging statements like debugger to debug JavaScript code.
62. What is error handling in JavaScript?
    • Error handling is the process of anticipating and responding to errors that may occur during the execution of a program. It involves catching and handling exceptions to prevent program crashes.
63. Explain the try…catch…finally statement in JavaScript.
    • The try...catch...finally statement is used for error handling in JavaScript. The try block contains the code that may throw an exception, the catch block handles the exception if one occurs, and the finally block executes code regardless of whether an exception was thrown.
64. What is the throw statement in JavaScript?
    • The throw statement is used to explicitly throw an exception. It can be used in conjunction with the try...catch statement to handle errors.
65. What is the console object in JavaScript?
    • The console object provides access to the browser’s debugging console and methods for logging messages, warnings, errors, and other information.
66. How can you log messages to the console in JavaScript?
    • You can use methods like console.log(), console.warn(), console.error(), and console.info() to log messages to the console.
67. What is the difference between console.log() and console.dir()?
    • console.log() is used to log a message to the console, while console.dir() is used to display an interactive list of the properties of a specified JavaScript object.
68. Explain the debugger statement in JavaScript.
    • The debugger statement is used to pause the execution of JavaScript code and start a debugging session. It can be placed anywhere in the code, and when encountered, it will cause the browser’s debugger to open.
69. What is source mapping in JavaScript debugging?
    • Source mapping is a technique used to map the generated code (e.g., minified or transpiled code) back to its original source code, making it easier to debug.
70. What are some common debugging techniques in JavaScript?
    • Some common debugging techniques include using breakpoints, stepping through code, inspecting variables, logging messages to the console, and using the browser’s developer tools.
71. What is the finally block in error handling?
    • The finally block is used to execute code, regardless of whether an exception is thrown or caught.
72. Explain the throw statement in JavaScript.
    • The throw statement allows you to throw an exception explicitly.

interview Questions for JavaScript Array Manipulation:

71. What are arrays in JavaScript?
    • Arrays are ordered collections of values, each identified by an index. They can contain values of any data type, including other arrays.
72. How can you create an array in JavaScript?
    • You can create an array using array literals ([]) or the Array() constructor.
73. Explain how you can access and modify elements in an array in JavaScript.
    • You can access elements in an array using bracket notation (array[index]), and you can modify elements by assigning new values to specific indices.
74. What are array methods in JavaScript?
    • Array methods are built-in functions that can be called on arrays to perform common operations such as adding or removing elements, iterating over elements, and transforming arrays.
75. What is the push() method in JavaScript?
    • The push() method adds one or more elements to the end of an array and returns the new length of the array.
76. What is the pop() method in JavaScript?
    • The pop() method removes the last element from an array and returns that element.
77. What is the shift() method in JavaScript?
    • The shift() method removes the first element from an array and returns that element, shifting all subsequent elements to a lower index.
78. What is the unshift() method in JavaScript?
    • The unshift() method adds one or more elements to the beginning of an array and returns the new length of the array.
79. Explain the splice() method in JavaScript.
    • The splice() method changes the contents of an array by removing or replacing existing elements and/or adding new elements in place.
80. What is the slice() method in JavaScript?
    • The slice() method returns a shallow copy of a portion of an array into a new array object selected from begin to end (end not included) where begin and end represent the index of items in that array.

interview Questions for JavaScript String Manipulation:

81. What are strings in JavaScript?
    • Strings are sequences of characters used to represent text. They can be created using string literals or the String() constructor.
82. How can you concatenate strings in JavaScript?
    • You can concatenate strings using the + operator or the concat() method.
83. What is the charAt() method in JavaScript?
    • The charAt() method returns the character at the specified index (position) in a string.
84. What is the split() method in JavaScript?
    • The split() method splits a string into an array of substrings based on a specified separator and returns the new array.
85. What is the substring() method in JavaScript?
    • The substring() method returns a subset of a string between two indices, not including the end index.
86. What is the substr() method in JavaScript?
    • The substr() method returns a substring of a string starting from a specified index and optionally including a specified number of characters.
87. What is the toUpperCase() method in JavaScript?
    • The toUpperCase() method returns the calling string value converted to uppercase.
88. What is the toLowerCase() method in JavaScript?
    • The toLowerCase() method returns the calling string value converted to lowercase.
89. What is the trim() method in JavaScript?
    • The trim() method removes whitespace from both ends of a string.
90. What is the replace() method in JavaScript?
    • The replace() method returns a new string with some or all matches of a pattern replaced by a replacement string.

interview Questions for JavaScript Regular Expressions (RegEx):

91. What are regular expressions in JavaScript?
    • Regular expressions are patterns used to match character combinations in strings. They are a powerful tool for text processing and manipulation.
92. How can you create a regular expression in JavaScript?
    • You can create a regular expression using the RegExp constructor or a literal notation (/pattern/flags).
93. What are flags in regular expressions?
    • Flags are optional parameters that modify the behavior of a regular expression (e.g., i for case-insensitive matching, g for global matching).
94. How do you use regular expressions in JavaScript?
    • Using methods like test(), exec(), match(), replace(), search(), and split().
95. Explain the test() method in JavaScript regular expressions.
    • The test() method executes a search for a match between a regular expression and a specified string. It returns true if a match is found, otherwise false.
96. Explain the exec() method in JavaScript regular expressions.
    • The exec() method executes a search for a match in a specified string. It returns an array containing the matched text if a match is found, otherwise null.
97. What are character classes in JavaScript regular expressions?
    • Character classes allow you to match any one of a range of characters. They are denoted by square brackets ([ ]) and can contain individual characters or ranges.
98. What are quantifiers in JavaScript regular expressions?
    • Quantifiers specify the number of occurrences of a character or group in a regular expression. They include * (zero or more), + (one or more), ? (zero or one), and {} (specific number of occurrences).
99. What are capturing groups in JavaScript regular expressions?
    • Capturing groups are portions of a pattern that are enclosed in parentheses. They allow you to extract and manipulate parts of a matched string.
100. What are lookahead and lookbehind assertions in JavaScript regular expressions?
     • Lookahead and lookbehind assertions are zero-length assertions that match a string only if it is followed or preceded by another string, respectively.
101. What are boundary matchers in JavaScript regular expressions?
     • Boundary matchers are used to match positions where specific boundaries occur in a string. They include ^ (start of string), $ (end of string), \b (word boundary), and \B (non-word boundary).
102. What are flags in JavaScript regular expressions?
     • Flags are optional parameters that modify the behavior of a regular expression. They are appended to the end of a regular expression literal and include i (case-insensitive), g (global match), and m (multiline).

interview Questions for JavaScript Browser APIs and DOM Manipulation:

101. What are browser APIs in JavaScript?
     • Browser APIs are sets of functions and methods provided by web browsers to interact with various aspects of the browser environment, such as the DOM, HTML5 features, CSS styling, and more.
102. Explain the localStorage and sessionStorage APIs in JavaScript.
     • localStorage and sessionStorage are web storage APIs that allow you to store key-value pairs locally in the browser. localStorage persists data even after the browser is closed, while sessionStorage data is cleared when the session ends (i.e., when the browser is closed).
103. What is the addEventListener() method in JavaScript?
     • The addEventListener() method is used to attach an event listener to an element. It takes an event type and a callback function as arguments and executes the callback when the specified event occurs on the element.
104. What is the fetch() API in JavaScript?
     • The fetch() API is used to make asynchronous HTTP requests in JavaScript. It returns a promise that resolves to the response to the request.
105. What is the XMLHttpRequest object in JavaScript?
     • The XMLHttpRequest object is a built-in browser object used to make HTTP requests in JavaScript. It provides an easy way to send and receive data from a web server asynchronously.
106. What are WebSockets in JavaScript?
     • WebSockets are a communication protocol that provides full-duplex communication channels over a single TCP connection. They enable real-time, bidirectional communication between a client and a server.
107. What is the Canvas API in JavaScript?
     • The Canvas API is a HTML5 feature that allows you to draw graphics and animations on a web page using JavaScript.
108. What is the Web Storage API in JavaScript?
     • The Web Storage API provides mechanisms by which browsers can store key/value pairs in a much more intuitive fashion than using cookies.
109. What is the File API in JavaScript?
     • The File API provides access to the contents of files using JavaScript, allowing web applications to read and manipulate files on the client’s system.
110. What is the Geolocation API in JavaScript?
     • The Geolocation API allows web applications to retrieve the geographical location information of a user’s device.

interview Questions for Miscellaneous in JavaScript:

111. What are polyfills in JavaScript?
     • Polyfills are pieces of code (usually JavaScript) that provide modern functionality on older browsers that do not natively support it.
112. What is the JavaScript event loop?
     • The event loop is a mechanism that allows JavaScript to perform non-blocking I/O operations by handling asynchronous callbacks in a single-threaded environment.
113. What are some common JavaScript performance optimization techniques?
     • Some common performance optimization techniques include minimizing DOM manipulation, reducing HTTP requests, optimizing JavaScript code, using caching techniques, and lazy-loading resources.
114. What are some security considerations when working with JavaScript?
     • Some security considerations include avoiding injection attacks (such as XSS and SQL injection), validating and sanitizing user input, using secure authentication and authorization mechanisms, and protecting sensitive data.
115. How can you improve the accessibility of a web application using JavaScript?
     • You can improve accessibility by ensuring proper semantic HTML markup, providing alternative text for images, implementing keyboard navigation, using ARIA roles and attributes, and testing with screen readers.
116. What are some best practices for writing clean and maintainable JavaScript code?
     • Some best practices include using meaningful variable and function names, following consistent coding style conventions, avoiding unnecessary global variables, modularizing code, commenting code where necessary, and writing unit tests.
117. How can you optimize website performance for mobile devices using JavaScript?
     • You can optimize performance for mobile devices by minimizing file sizes (e.g., JavaScript, CSS, and images), using responsive design techniques, lazy-loading resources, minimizing DOM manipulation, and testing on real mobile devices.
118. What are some JavaScript design patterns, and when would you use them?
     • Some common design patterns include Singleton, Module, Factory, Observer, and MVC. You would use design patterns to solve recurring design problems and improve code maintainability, scalability, and reusability.
119. What are some tools and libraries commonly used in JavaScript development?
     • Some common tools and libraries include package managers (such as npm and Yarn), task runners (such as Gulp and Grunt), build tools (such as webpack and Babel), testing frameworks (such as Jest and Mocha), and front-end libraries and frameworks (such as React, Angular, and Vue.js).
120. Explain the difference between cookies, localStorage, and sessionStorage.
     • Cookies are small pieces of data stored in the browser that are sent with every HTTP request. They have a limited size (typically 4KB) and are sent to the server with every request, which can impact performance. localStorage and sessionStorage are newer web storage APIs that allow larger amounts of data (up to 5MB) to be stored locally in the browser. localStorage data persists even after the browser is closed, while sessionStorage data is cleared when the session ends (i.e., when the browser is closed).

interview Questions for JavaScript AJAX and Fetch API:

121. What is AJAX in JavaScript?
     • AJAX (Asynchronous JavaScript and XML) is a technique for updating parts of a web page without reloading the whole page.
122. How do you make AJAX requests in JavaScript?
     • Using the XMLHttpRequest object or the newer fetch() API.
123. What is the Fetch API in JavaScript?
     • The Fetch API provides an interface for fetching resources asynchronously across the network.
124. How do you use the Fetch API to make HTTP requests?
     • By calling the fetch() function with the URL of the resource you want to fetch.
125. What are promises in the Fetch API?
     • Promises are used to handle the results of asynchronous operations in the Fetch API.
126. How do you handle errors in Fetch API requests?
     • By chaining a .catch() method to the promise returned by the fetch() function.

interview Questions for JavaScript Local Storage and Cookies:

127. What is local storage in JavaScript?
     • Local storage is a mechanism that allows web applications to store data locally within the user’s browser.
128. How do you use local storage in JavaScript?
     • By using the localStorage object, which provides methods like setItem(), getItem(), removeItem(), and clear().
129. What are cookies in JavaScript?
     • Cookies are small pieces of data stored on the client’s browser by websites.
130. How do you create and read cookies in JavaScript?
     • By setting cookie values using the document.cookie property and reading them from the same property.
131. What are the differences between local storage and cookies?
     • Local storage has a larger storage capacity than cookies.
     • Local storage data is not sent with every HTTP request, while cookies are.
     • Local storage data is stored indefinitely, while cookies can have expiration dates.

interview Questions for JavaScript Testing:

132. What is unit testing in JavaScript?
     • Unit testing is the process of testing individual units or components of a software application in isolation.
133. How do you write unit tests in JavaScript?
     • Using testing frameworks like Jasmine, Mocha, or Jest, and assertion libraries like Chai or Expect.
134. What is test-driven development (TDD)?
     • Test-driven development is a software development process where tests are written before the code is implemented.
135. What is mocking in JavaScript testing?
     • Mocking is the process of creating simulated versions of objects or functions in order to test the behavior of other objects or functions.
136. What is code coverage in JavaScript testing?
     • Code coverage is a measure used to describe the degree to which the source code of a program has been tested.

interview Questions for JavaScript Debugging:

137. How do you debug JavaScript code?
     • Using browser developer tools like Chrome DevTools or Firefox Developer Tools.
     • By inserting console.log() statements into the code.
138. What are breakpoints in JavaScript debugging?
     • Breakpoints are points in the code where execution will pause so that you can inspect the state of the program.
139. How do you set breakpoints in JavaScript code?
     • By clicking on the line number in the source code or using the debugger statement.

interview Questions for JavaScript Performance Optimization:

140. What are some common performance issues in JavaScript?
     • Inefficient DOM manipulation, excessive memory usage, long-running JavaScript code, blocking operations, etc.
141. How do you optimize JavaScript performance?
     • Minifying and compressing JavaScript code.
     • Reducing DOM manipulation.
     • Optimizing images and other media files.
142. What is lazy loading in JavaScript?
     • Lazy loading is a technique where resources are loaded only when they are needed, rather than all at once.
143. How do you implement lazy loading in JavaScript?
     • By deferring the loading of non-critical resources until they are needed, often using Intersection Observer API or custom JavaScript.

interview Questions for JavaScript Security:

144. What are some common security vulnerabilities in JavaScript?
     • Cross-site scripting (XSS), Cross-site request forgery (CSRF), SQL injection, insecure direct object references, etc.
145. How do you prevent XSS attacks in JavaScript?
     • By properly escaping user input, validating and sanitizing data, and using Content Security Policy (CSP) headers.
146. What is Content Security Policy (CSP) in JavaScript?
     • CSP is a security standard that helps prevent XSS attacks by allowing website administrators to control which resources can be loaded and executed on their web pages.
147. How do you handle authentication and authorization in JavaScript applications?
     • By using techniques like JSON Web Tokens (JWT), OAuth, and session management.

interview Questions for JavaScript Frameworks and Libraries:

148. What are some popular JavaScript frameworks and libraries?
     • React, Angular, Vue.js, jQuery, Bootstrap, Express.js, Node.js, etc.
149. What is React and how does it differ from other frameworks?
     • React is a JavaScript library for building user interfaces. It uses a virtual DOM and a component-based architecture.
150. What is Angular and how does it differ from React?
     • Angular is a JavaScript framework for building single-page applications. It provides a full-featured MVC architecture and two-way data binding.
151. What is Vue.js and how does it differ from React and Angular?
     • Vue.js is a progressive JavaScript framework for building user interfaces. It is more lightweight and easier to learn than React and Angular.
152. How do you choose between different JavaScript frameworks and libraries?
     • It depends on factors like project requirements, team expertise, performance, community support, and ecosystem.
153. What are some advantages of using JavaScript frameworks and libraries?
     • They provide pre-built components and tools for building applications faster.
     • They have active communities and ecosystems with extensive documentation and resources.
154. What are some disadvantages of using JavaScript frameworks and libraries?
     • They may introduce a learning curve for developers.
     • They can add overhead to the application size and complexity.

JavaScript Interview Tips:

1. Practice coding regularly to improve your problem-solving skills.
2. Review common algorithms and data structures used in JavaScript.
3. Be prepared to discuss your previous projects and experiences.
4. Stay updated on the latest developments in JavaScript and web development.
5. Ask questions during the interview to demonstrate your interest and understanding.

Conclusions

This comprehensive list covers various aspects of JavaScript that are commonly asked in interviews for full-stack web development positions. Make sure to understand each concept thoroughly and practice coding examples to solidify your understanding. Good luck with your interviews!