ES6 Interview Questions and Answers for 7 years experience

0
ES6 Interview Questions & Answers

  1. What are the key features of ES6 (ECMAScript 2015)?

    • Answer: ES6 introduced numerous significant features, including arrow functions, classes, modules, let and const for block scoping, template literals, destructuring, promises, iterators and generators, Map and Set objects, and more. These features greatly improved JavaScript's expressiveness, maintainability, and performance.

  2. Explain arrow functions and their advantages.

    • Answer: Arrow functions provide a concise syntax for writing functions. They lexically bind `this`, eliminating the need for `bind`, `call`, or `apply` in many cases. They also implicitly return single-expression values. Advantages include cleaner code and improved `this` handling.

  3. Describe the difference between `let`, `const`, and `var`.

    • Answer: `var` has function scope, while `let` and `const` have block scope. `const` declares a constant, meaning its value cannot be reassigned after initialization. `let` allows reassignment but is still block-scoped.

  4. What are template literals? Give an example.

    • Answer: Template literals use backticks (`) to define strings, allowing embedded expressions using `${expression}`. They simplify string interpolation. Example: `let name = "John"; console.log(`Hello, ${name}!`);`

  5. Explain destructuring assignment. Provide examples for objects and arrays.

    • Answer: Destructuring allows extracting values from objects and arrays into distinct variables. Object example: `const {name, age} = {name: "John", age: 30};`. Array example: `const [first, second] = [10, 20];`.

  6. How do Promises work? Explain their states and how to handle them.

    • Answer: Promises represent the eventual result of an asynchronous operation. They have three states: pending, fulfilled (resolved), and rejected. `.then()` handles fulfilled promises, and `.catch()` handles rejected promises. `.finally()` executes regardless of the outcome.

  7. What are async/await functions? How do they improve asynchronous code readability?

    • Answer: `async/await` makes asynchronous code look and behave a bit more like synchronous code, improving readability. `async` declares an asynchronous function, and `await` pauses execution until a Promise resolves.

  8. Explain the difference between `Map` and `Object` in ES6.

    • Answer: While both store key-value pairs, `Map` allows any data type as a key (including objects), whereas `Object` keys are always strings (or Symbols). `Map` also provides methods like `size`, `has`, `get`, `set`, `delete`, and iteration methods, offering more robust functionality than plain objects for key-value storage.

  9. What are Sets in ES6? How are they different from arrays?

    • Answer: Sets store unique values of any type. Unlike arrays, they do not allow duplicate elements. They offer methods for adding, removing, and checking for the existence of elements.

  10. Explain how modules work in ES6.

    • Answer: ES6 modules provide a way to structure code into reusable modules using `import` and `export` statements. `export` makes variables, functions, or classes available to other modules, while `import` brings them in.

  11. What are iterators and generators in ES6?

    • Answer: Iterators provide a standard way to traverse data structures. Generators are special functions that can be paused and resumed, making them useful for creating iterators and handling asynchronous operations.

  12. Explain the concept of classes in ES6. How do they differ from function constructors?

    • Answer: ES6 classes provide a syntactic sugar over the prototype-based inheritance system in JavaScript. They offer a cleaner and more readable way to define classes and inheritance compared to function constructors, utilizing keywords like `class`, `extends`, and `super`.

  13. How do you handle errors in ES6 using `try...catch`?

    • Answer: The `try...catch` block handles exceptions. Code that might throw an error is placed in the `try` block, and the `catch` block handles any errors that occur, allowing for graceful error handling and preventing application crashes.

  14. What is the spread syntax (...)? Give examples of its use.

    • Answer: The spread syntax allows expanding iterable objects into individual elements. It can be used to copy arrays (`[...arr]`), concatenate arrays (`[...arr1, ...arr2]`), and pass arguments to functions (`func(...args)`).

  15. What is the rest parameter syntax (...)? Give examples of its use.

    • Answer: The rest parameter syntax gathers multiple arguments into a single array. It's useful for creating functions that accept a variable number of arguments. Example: `function sum(...numbers) { return numbers.reduce((a, b) => a + b, 0); }`

  16. Explain Symbol data type.

    • Answer: Symbols are unique and immutable values, often used as unique object keys to avoid naming collisions.

  17. What are Proxies in ES6?

    • Answer: Proxies intercept operations performed on an object, allowing you to customize how the object behaves. They're useful for creating custom getters, setters, and more.

  18. What are Reflect APIs?

    • Answer: Reflect APIs provide methods to perform operations on objects and proxies in a more structured way, offering a cleaner alternative to direct object manipulation.

  19. Explain how to use `Object.assign()` method.

    • Answer: `Object.assign()` copies the values of all enumerable own properties from one or more source objects to a target object. It returns the target object.

  20. Describe `Object.keys()`, `Object.values()`, and `Object.entries()`.

    • Answer: `Object.keys()` returns an array of an object's own enumerable property names. `Object.values()` returns an array of an object's own enumerable property values. `Object.entries()` returns an array of an object's own enumerable property [key, value] pairs.

  21. Explain the difference between `==` and `===` in JavaScript.

    • Answer: `==` performs loose equality comparison, performing type coercion if necessary. `===` performs strict equality comparison, requiring both value and type to be identical.

  22. What is hoisting in JavaScript? How does it work with `let` and `const`?

    • Answer: Hoisting moves variable and function declarations to the top of their scope before code execution. However, with `let` and `const`, the variables are not initialized until their declaration is reached, resulting in a `ReferenceError` if accessed before the declaration.

  23. Explain the concept of closures in JavaScript.

    • Answer: A closure is a function that has access to variables from its surrounding lexical environment, even after that environment has finished executing.

  24. What are the benefits of using modules in large JavaScript applications?

    • Answer: Modules improve code organization, reusability, maintainability, and prevent naming conflicts in large applications by promoting modularity and encapsulation.

  25. How can you prevent memory leaks in JavaScript?

    • Answer: Techniques include removing event listeners, clearing intervals and timeouts, and avoiding circular references.

  26. Explain the concept of `this` keyword in JavaScript.

    • Answer: The `this` keyword refers to the object that owns the currently executing code. Its value depends on how the function is called (e.g., method invocation, function invocation, etc.).

  27. How would you handle asynchronous operations in a large application?

    • Answer: Using Promises, async/await, or libraries like RxJS for managing asynchronous flows and handling errors effectively.

  28. What are some best practices for writing clean and maintainable JavaScript code?

    • Answer: Using consistent coding style, meaningful variable names, modular design, proper commenting, and utilizing linters/formatters.

  29. Explain the difference between synchronous and asynchronous programming.

    • Answer: Synchronous programming executes code line by line, while asynchronous programming allows for concurrent execution of multiple operations, improving responsiveness.

  30. What are some common JavaScript design patterns?

    • Answer: Examples include Module, Singleton, Observer, Factory, and many more.

  31. How do you debug JavaScript code?

    • Answer: Using browser developer tools (console logging, breakpoints, stepping through code), linters, and debuggers.

  32. What are some performance optimization techniques for JavaScript?

    • Answer: Minimizing DOM manipulations, using efficient algorithms, code splitting, lazy loading, and caching.

  33. Explain the concept of event delegation.

    • Answer: Attaching event listeners to a parent element instead of individual child elements, improving performance and reducing memory usage.

  34. What are some common JavaScript libraries or frameworks you have used?

    • Answer: React, Angular, Vue, jQuery (and explain experience with each)

  35. How do you test your JavaScript code?

    • Answer: Unit testing (Jest, Mocha, Jasmine), integration testing, end-to-end testing (Cypress, Selenium).

  36. Describe your experience with working in a team environment on JavaScript projects.

    • Answer: (Describe collaborative experiences, version control, code reviews, etc.)

  37. Explain your process for learning new JavaScript technologies or frameworks.

    • Answer: (Describe personal learning methods, resources used, etc.)

  38. How do you stay up-to-date with the latest developments in JavaScript?

    • Answer: (Mention blogs, conferences, newsletters, online courses, etc.)

  39. Describe a challenging JavaScript problem you encountered and how you solved it.

    • Answer: (Describe a specific problem and the solution, highlighting problem-solving skills.)

  40. What are your strengths and weaknesses as a JavaScript developer?

    • Answer: (Be honest and provide specific examples.)

  41. Why are you interested in this position?

    • Answer: (Relate your skills and interests to the specific job description.)

  42. Where do you see yourself in 5 years?

    • Answer: (Show ambition and career goals.)

Thank you for reading our blog post on 'ES6 Interview Questions and Answers for 7 years experience'.We hope you found it informative and useful.Stay tuned for more insightful content!