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// Implement debounce
function debounce(fn, wait) {
let timer;
return function (...args) {
clearTimeout(timer);
timer = setTimeout(() => {
fn.apply(this, args);
}, wait);
};
}Real environment, not a toy
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Multi-framework, one question
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Same question. Four frameworks.
Practice in the stack your interview demands. Switch frameworks any time — your progress saves per variant.
import { useState } from 'react';
export function Accordion({ items }: { items: Item[] }) {
const [openId, setOpenId] = useState<string | null>(null);
return (
<ul className="accordion">
{items.map((item) => (
<li key={item.id}>
<button onClick={() => setOpenId(openId === item.id ? null : item.id)}>
{item.label}
</button>
{openId === item.id && <div>{item.content}</div>}
</li>
))}
</ul>
);
}Solutions that explain the why.
Diagrams, edge-case callouts, and step-by-step walkthroughs. Not just a code dump.
function debounce(fn, wait) {
let timer;
return function (...args) {
clearTimeout(timer);
timer = setTimeout(
() => fn.apply(this, args),
wait
);
};
}Use setTimeout and clear the timer on each call. That's it.
Picture a user mashing a search box. Each keystroke is a call; you want the request to fire only after they pause. The timer resets on every call — like constantly punching the snooze button.
this binds to the call site — interview gotcha that catches most candidates.640+ questions. Real interview questions.
Curated from real interview leaks. Easy warmups to staff-level system design.
Debounce
Implement a function that delays invoking another function until a specified period of inactivity has passed.
Throttle
Implement a function that limits how often a wrapped function can be invoked within a time window.
Accordion
Build an accordion component with stacked sections whose content panels expand and collapse on click.
Todo List
Build a Todo List component with add and delete actions, with focus on functionality over styling.
Array.prototype.myReduce
PREMIUMImplement Array.prototype.myReduce — the reduce method from scratch, including the empty-array + initial-value edge cases.
A/B Test Bucketing
Assign users to weighted experiment variants deterministically, with a traffic gate and independent buckets per experiment.
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