ES6 Interview Questions and Answers for 10 years experience

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

   • Answer: ES6 introduced many significant features, including arrow functions, classes, modules, `let` and `const` (block-scoped variables), destructuring, template literals, promises, iterators and generators, Maps and Sets, and more. These features significantly improved JavaScript's capabilities and readability.

2. Explain arrow functions and their advantages over traditional function expressions.

   • Answer: Arrow functions provide a concise syntax for writing functions. They lexically bind `this`, simplifying handling of `this` within callbacks and methods. They also implicitly return single-expression values, making them more compact. However, they lack their own `this`, `arguments`, and `new.target` bindings.

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

   • Answer: `var` is function-scoped, while `let` and `const` are block-scoped. `const` declares a constant value that cannot be reassigned, while `let` allows reassignment. Using `let` and `const` promotes better code readability and prevents accidental variable reassignments.

4. What is destructuring and how does it simplify code?

   • Answer: Destructuring allows you to unpack values from arrays or objects into distinct variables. This eliminates the need for multiple assignment statements, making code more concise and readable. It can be used with both arrays and objects, and even nested objects.

5. Explain template literals and their benefits.

   • Answer: Template literals use backticks (`) to define strings, allowing embedded expressions using `${}`. They improve string formatting, enabling multiline strings and easy interpolation of variables and expressions directly within the string, improving readability.

6. How do Promises work and what are their advantages over callbacks?

   • Answer: Promises represent the eventual result of an asynchronous operation. They handle asynchronous code more cleanly than callbacks, avoiding "callback hell" by using `.then()` for chaining asynchronous operations and `.catch()` for error handling. They improve code readability and maintainability for asynchronous tasks.

7. What are iterators and generators? Give examples.

   • Answer: Iterators provide a standardized way to traverse data structures. Generators are a special type of function that can pause execution and resume later, yielding values one at a time. They are useful for creating custom iterators and handling large datasets efficiently.

8. Explain the differences between Maps and Sets.

   • Answer: Maps store key-value pairs, similar to Objects, but allow any data type as keys. Sets store unique values of any data type. Maps are suitable for key-value data, while Sets are ideal for managing unique collections of items.

9. What are classes in ES6 and how do they differ from prototype-based inheritance?

   • Answer: ES6 classes provide a syntactic sugar over JavaScript's prototype-based inheritance. They offer a more familiar class-based syntax, simplifying object-oriented programming concepts. Under the hood, they still use prototypes, but the syntax is cleaner and easier to understand.

10. Explain modules in ES6 and how they improve code organization.

    • Answer: ES6 modules allow you to break down code into reusable modules, improving code organization and maintainability. They support explicit imports and exports, promoting better code structure and reducing naming conflicts.

11. How do you handle asynchronous operations using async/await?

    • Answer: `async/await` makes asynchronous code look and behave a bit more like synchronous code, making it easier to read and reason about. The `async` keyword designates an asynchronous function, and `await` pauses execution until a Promise resolves.

12. What are rest parameters and spread syntax? Provide examples.

    • Answer: Rest parameters (`...`) allow a function to accept an indefinite number of arguments as an array. Spread syntax (`...`) expands iterable objects (arrays, strings, etc.) into individual elements. They are useful for flexible function arguments and array manipulation.

13. Explain the concept of `Symbol` in ES6.

    • Answer: Symbols are unique and immutable data types. They are useful for creating unique property keys on objects, preventing naming collisions, and creating private properties.

14. What are Proxies and how can they be used?

    • Answer: Proxies intercept operations (get, set, deleteProperty, etc.) on an object. They allow you to add custom behavior to object access, such as logging, validation, or data transformation.

15. How do you implement inheritance using ES6 classes?

    • Answer: Inheritance is achieved using the `extends` keyword. A subclass inherits properties and methods from its superclass, and can override or extend them.

16. Explain the use of `super` keyword in ES6 classes.

    • Answer: The `super` keyword refers to the parent class. It's used to call the constructor or methods of the parent class from within a subclass.

17. What is the difference between `Object.assign()` and the spread operator for merging objects?

    • Answer: Both merge objects, but the spread operator creates a shallow copy, while `Object.assign()` also performs a shallow copy but modifies the target object directly. The spread operator is generally preferred for its readability.

18. How can you create a private class member in ES6? (Discuss workarounds)

    • Answer: ES6 doesn't have true private members. Workarounds involve using WeakMaps or naming conventions (e.g., prefixing private members with an underscore) to indicate private access. However, these are conventions, not enforced by the language.

19. Describe how to handle errors using try...catch blocks.

    • Answer: `try...catch` blocks handle runtime exceptions. Code that might throw an error is placed in the `try` block, and the `catch` block handles the error if one occurs, preventing the program from crashing.

20. Explain the concept of closures in JavaScript, and how they relate to ES6.

    • Answer: Closures are functions that have access to variables from their surrounding lexical environment, even after that environment has finished executing. ES6 doesn't change the core concept of closures, but features like arrow functions can affect how `this` is bound within a closure.

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