Summary
I interviewed for a Senior UI Developer position at Arctic Wolf, undergoing five rounds. Despite receiving positive feedback after the initial four rounds and anticipating an offer, I was ultimately rejected following the final technical round due to the interviewer's feedback on my complex solution to a problem they considered simple.
Full Experience
My interview process for the Senior UI Developer role at Arctic Wolf consisted of five comprehensive rounds.
Round 1: JavaScript Fundamentals
This round lasted 60 minutes and focused heavily on core JavaScript concepts. I was asked to explain closures and provide code examples. I also had to implement debounce and throttle functions from scratch using vanilla JavaScript. Promises were a significant topic, where I explained their purpose and wrote a polyfill for Promise.all(). Several questions involved predicting the output of complex JavaScript code snippets related to promise chains, the this keyword behavior, the event loop and microtasks, the differences between var and let in loops, and hoisting and variable scope. Finally, I was tasked with writing a polyfill for Array.prototype.reduce.
Round 2: Machine Coding
This 60-minute round was a practical coding challenge. My primary task was to build a To-Do List Application. It needed to have three filter tabs (Completed, In Progress, Deleted), display tasks based on the selected filter, and handle keyboard interactions, such as adding a new task on an Enter key press. After completing the main task early, I was given an additional question to determine the output of another promise chain code snippet.
Round 3: System Design
My 60-minute round with a Lead Engineer started with a detailed discussion about my past projects. Then, we moved into optimization techniques, specifically virtualization and lazy loading. I was asked to write pseudo-code to implement virtualization using vanilla JavaScript and the Intersection Observer API. We also discussed React performance, including the React Profiler and its usage, and explored micro-frontend architecture in theory.
Round 4: Hiring Manager
My 60-minute discussion with the Engineering Manager covered my career journey and background. Interestingly, despite my UI-focused profile, we delved into system design topics like message queues. I was also asked about implementing a role-based authentication application and how to manage page visibility based on user roles. The round concluded with standard behavioral and cultural fit questions.
Round 5: Final Tech Round
Before this round, the recruiter had informed me that all previous rounds had positive feedback, and an offer letter was expected soon. However, on Monday, I was scheduled for an unexpected fifth round focused on design and coding. This round began with an introduction and a project discussion, where I explained the migration from Gatsby to React at Fairmatic and answered follow-up questions on design choices and collaboration. The main challenge was a React coding question based on async behavior. I misunderstood the question and implemented a complex solution, which technically worked. The interviewer then asked for a simpler solution, which I unfortunately couldn't provide during the interview time.
Outcome
Despite clearing the initial four rounds with positive feedback and being told an offer was imminent, I received a 'Do Not Proceed' feedback from the 5th round interviewer. This led to my rejection, which was quite frustrating, especially given the prior positive indicators. I was surprised by the negative feedback because my solution, though complex, was functional. I heard that others usually only had a maximum of 3 rounds, but my role for the main platform team required 5 rounds.
Interview Questions (16)
Explain what closures are in JavaScript and provide relevant code examples to demonstrate their concept and usage.
Implement the debounce and throttle functions in vanilla JavaScript.
Explain what promises are in JavaScript and write a polyfill for the Promise.all() method.
Predict the console output of the following JavaScript promise chain:
Promise.resolve(1)
.then((val) => {
console.log(val);
return val + 1;
})
.then((val) => {
console.log(val);
})
.then((val) => {
console.log(val);
return Promise.resolve(3).then((val) => {
console.log(val);
});
})
.then((val) => {
console.log(val);
return Promise.reject(4);
})
.catch((val) => {
console.log(val);
})
.finally((val) => {
console.log(val);
return 10;
})
.then((val) => {
console.log(val);
});
Predict the console output of the following JavaScript code snippet, focusing on the behavior of the this keyword in different function contexts:
const obj = {
dev: "bfe",
a: function () {
return this.dev;
},
b() {
return this.dev;
},
c: () => {
return this.dev;
},
d: function () {
return (() => {
return this.dev;
})();
},
e: function () {
return this.b();
},
f: function () {
return this.b;
},
g: function () {
return this.c();
},
h: function () {
return this.c;
},
i: function () {
return () => {
return this.dev;
};
},
};
console.log(obj.a());
console.log(obj.b());
console.log(obj.c());
console.log(obj.d());
console.log(obj.e());
console.log(obj.f()());
console.log(obj.g());
console.log(obj.h()());
console.log(obj.i()());
Predict the console output of the following JavaScript code snippet, demonstrating understanding of the event loop and microtask queue:
console.log(1);
const promise = new Promise((resolve) => {
console.log(2);
resolve();
console.log(3);
});
console.log(4);
promise
.then(() => {
console.log(5);
})
.then(() => {
console.log(6);
});
console.log(7);
setTimeout(() => {
console.log(8);
}, 10);
setTimeout(() => {
console.log(9);
}, 0);
Predict the console output of the following JavaScript code snippets, illustrating the differences between var and let in loop scopes:
for (var i = 0; i < 5; i++) {
setTimeout(() => console.log(i), 0);
}
for (let i = 0; i < 5; i++) {
setTimeout(() => console.log(i), 0);
}
Predict the console output of the following JavaScript code snippet, demonstrating understanding of hoisting and variable scope:
var a = 1;
function func() {
a = 2;
console.log(a);
var a;
}
func();
console.log(a);
if (!("b" in window)) {
var b = 1;
}
console.log(b);
Write a polyfill for the Array.prototype.reduce method in JavaScript.
Build a To-Do List Application with the following requirements:
- Three filter tabs: Completed, In Progress, and Deleted
- Display tasks based on the selected filter
- Handle keyboard interactions (e.g., add new task on Enter key press)
Predict the console output of the following JavaScript promise chain:
Promise.resolve(1)
.then(() => 2)
.then(3)
.then((value) => value * 3)
.then(Promise.resolve(4))
.then(console.log);
Explain virtualization and lazy loading, and then write pseudo-code to implement virtualization with vanilla JavaScript using the Intersection Observer API.
Discuss React Profiler and its usage for performance optimization in React applications.
Explain the theoretical knowledge of micro-frontend architecture.
Discuss message queues in the context of system design, even for a UI-focused profile.
Explain how to implement a role-based authentication application and how to show pages based on user roles.