What is the difference between "undefined" and "null"
in JavaScript?
In JavaScript, "undefined" is a primitive value
that indicates the absence of a value or uninitialized variable, while "null" is
also a primitive value that represents the intentional absence of any object value.
"undefined" is the default value for uninitialized variables, whereas "null" is a
value that can be assigned to a variable explicitly.
What is the purpose of the "this" keyword in
JavaScript?
The "this" keyword refers to the current
execution context and is used to access object properties and methods within that
context. It allows dynamic binding and enables flexible code reuse in
object-oriented programming. The value of "this" depends on how a function is called
or how an object is accessed.
Explain the concept of closures in JavaScript.
Closures are a combination of functions and
the lexical environment within which they were declared. They allow functions to
retain access to variables from their parent scopes even after the parent function
has finished executing. Closures are commonly used to create private variables,
implement data encapsulation, and enable higher-order functions.
What are the differences between "let," "const," and
"var" in JavaScript?
"let" and "const" are block-scoped variables
introduced in ES6, while "var" is function-scoped. "let" and "const" variables have
block-level scope, meaning they are limited to the block of code they are defined
in, while "var" variables are hoisted to the top of their scope. "const" variables
cannot be reassigned once defined, whereas "let" and "var" variables can be
reassigned.
How does prototypal inheritance work in JavaScript?
JavaScript uses prototypal inheritance, where
objects inherit properties and methods from their prototype objects. Each object has
an internal link to its prototype, and if a property or method is not found in the
object itself, it is looked up in the prototype chain. This allows for efficient
code reuse and the ability to create object hierarchies.
How would you handle an asynchronous operation in
JavaScript?
The candidate should mention using techniques
like callbacks, Promises, or async/await. They should explain how they would
structure their code to handle asynchronous operations, handle errors, and ensure
proper sequencing or parallelism.
Describe your approach to optimizing the performance
of JavaScript code.
The candidate should discuss techniques like
minimizing DOM manipulation, optimizing loops, reducing unnecessary computations,
using efficient data structures, implementing caching mechanisms, leveraging web
workers or service workers for background tasks, and utilizing performance profiling
tools.
Suppose you encounter a critical bug in a JavaScript
application that is affecting production. How would you handle it?
The candidate should mention steps like
identifying the root cause of the bug, creating a minimal reproducible test case,
fixing the issue with proper testing and validation, coordinating with other team
members or stakeholders, deploying the fix, and implementing preventive measures to
avoid similar issues in the future.
How would you handle cross-browser compatibility
issues in JavaScript development?
The candidate should mention strategies like
using feature detection instead of browser detection, implementing polyfills or
shims for missing functionalities, utilizing CSS frameworks or libraries that handle
cross-browser compatibility, and testing the application on different browsers and
versions.
Describe your process for debugging JavaScript code.
The candidate should explain their approach to
debugging, including techniques like using browser developer tools, console logging,
setting breakpoints, analyzing stack traces and error messages, utilizing debugging
extensions or tools, and implementing unit tests or integration tests.
Can you describe a challenging JavaScript project you
worked on? How did you overcome the difficulties?
The candidate should provide an example of a
complex JavaScript project they were involved in, describe the specific challenges
faced, and explain the actions they took to overcome those challenges. This question
evaluates problem-solving skills and adaptability.
Tell us about a time when you had to work
collaboratively with a team to deliver a JavaScript project. How did you contribute
to the team's success?
The candidate should share an experience where
they collaborated with team members, participated in code reviews, provided
constructive feedback, communicated effectively, and adapted to team processes and
requirements. They should highlight their teamwork and communication skills.
How do you stay up-to-date with the latest trends and
updates in the JavaScript ecosystem?
The candidate should discuss their approach to
continuous learning, such as following JavaScript-related blogs and newsletters,
participating in online communities or forums, attending conferences or meetups, and
engaging in personal projects to explore new JavaScript frameworks or libraries.
Describe a situation where you had to refactor
existing JavaScript code to improve its maintainability or performance. What steps
did you take, and what was the outcome?
The candidate should share an experience where
they refactored JavaScript code to enhance its readability, modularity, or
performance. They should explain the techniques used, the challenges faced during
refactoring, and the positive impact the refactoring had on the codebase.
Can you describe a time when you had to explain
complex JavaScript concepts or solutions to a non-technical stakeholder? How did you
ensure effective communication?
The candidate should provide an example where
they had to communicate technical concepts to non-technical stakeholders. They
should explain how they simplified complex ideas, used analogies or visual aids, and
adapted their communication style to ensure clear understanding and alignment with
stakeholders' expectations.
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