How to Hire a Frontend Developer in 2026: CSS, Performance, and Skills Beyond React

“Frontend developer” is one of the most inconsistently screened roles in software. At some companies it means React developer. At others it means someone who can build pixel-perfect layouts with clean CSS from scratch. At a few it means both. The gap between those definitions is wide enough that a screen designed for one will miss the other entirely.

The problem is that most job descriptions do not decide which one they need, and the interviews do not clarify it either. The result is either over-reliance on framework knowledge that does not tell you much, or generic algorithm questions that test almost nothing relevant.

Here is what a useful screen actually looks at.

The platform first, the framework second

In 2026, React, Vue, Angular, and Svelte are all legitimate choices. A developer who understands how the browser works will function well in any of them. A developer who knows React cold but has a shallow model of how the DOM actually behaves will struggle when the framework does not solve the problem for them.

So the screen should start with browser fundamentals and treat framework knowledge as a secondary filter.

CSS: the clearest signal

CSS fluency is the quickest way to separate frontend developers from people who copy and paste from Stack Overflow. And the specific questions matter more than people think.

Start with layout. Ask them to explain how they would build a sidebar layout where the sidebar is fixed-width and the content fills the remaining space, and the whole thing collapses to a single column on mobile. You want to hear about Flexbox or Grid, min-width, flex-shrink, and media queries. Someone who says “I would use a framework like Tailwind” is telling you they solve layout with utility classes, not that they understand the underlying model.

Follow with specificity. “What is the difference between a class selector and an ID selector in terms of CSS specificity?” The answer: ID selectors have higher specificity (100 points in the old 0-1-0-0 model), which is why over-using IDs makes CSS hard to override and maintain. A developer who cannot articulate this has not reasoned about cascade; they have just written CSS until it worked.

Then ask about display: contents. It is not an advanced trick, but it is specific enough to reveal someone who has actually read the CSS spec or debugged layout issues in depth. The correct answer: it makes a box participate in the formatting context of its parent rather than establishing its own, effectively removing the element from the layout tree while keeping its children. Developers who understand this concept understand the box model well.

Custom properties (CSS variables) are now baseline. Ask how they differ from preprocessor variables like Sass $variables. The answer: CSS custom properties are live in the browser, can be changed with JavaScript, cascade through the DOM, and can reference each other dynamically. Sass variables compile away before the browser sees them.

HTML semantics and accessibility

Most teams undertest this. The surface area of HTML is small, but the implications of getting it wrong are real: broken keyboard navigation, missing screen reader announcements, and behavior that breaks in unexpected browsers.

Ask: “What does a <button> element do that a <div onclick> does not?” A correct answer covers at least: keyboard focus and activation (Enter and Space), default ARIA role of button, participation in form submission when inside a form, and the ability to be disabled via the disabled attribute. Getting four out of four is a signal that the candidate has actually thought about how the browser implements interactive elements.

Ask them to describe when they would use <article>, <section>, and <div>. There is no single right answer, but a developer who says “I mostly use divs and add classes” has not internalized semantic markup. A developer who explains that <article> signals self-contained content that makes sense in isolation (and that screen readers and feed parsers use this), and <section> groups thematically related content within a page, is working from a real mental model.

Core Web Vitals: expected knowledge in 2026

Google’s Core Web Vitals are ranking signals and real user experience metrics. A senior frontend engineer should understand all three without looking them up.

LCP (Largest Contentful Paint) is the time until the main visible element loads. The most common culprits: large unoptimized hero images, late-loaded fonts causing a flash, or render-blocking resources in the head. Fixes include <link rel="preload"> for critical assets, responsive image sizing, AVIF or WebP formats, and moving render-blocking scripts.

INP (Interaction to Next Paint) replaced FID in March 2024. It measures the worst 98th percentile interaction latency across the entire page session. Long JavaScript tasks are the main cause. The fix is usually breaking up large synchronous work with scheduler.yield() or splitting tasks with setTimeout(0).

CLS (Cumulative Layout Shift) catches elements that move unexpectedly because their size was not reserved. The classic case: an image without explicit width and height attributes that causes content below it to shift when it loads.

If a candidate cannot name the three metrics and give a plausible fix for each, they have not worked on a performance-sensitive product recently. That is fine for a junior role, but it is a gap at senior level.

JavaScript fundamentals

Framework knowledge is not a proxy for JavaScript knowledge. Test the language, not the library.

Ask about closures with a practical example: “What does this function return and why?” Pass them code where a variable is captured in a closure inside a loop. The subtle behavior here (shared binding vs. captured value) is something a developer who understands execution context and scope gets right, and someone who has only used React hooks gets wrong.

Ask about async/await and what it does under the hood. The answer should mention the event loop, that async functions return Promises, and that await yields execution to the event loop until the Promise settles. Bonus: ask what happens if you await two independent promises sequentially instead of with Promise.all, and why it matters for performance.

Ask about event delegation: attaching a single listener to a parent element and using event.target to identify which child was clicked. Why: reduces listener count in list-heavy UIs and handles dynamically added elements. A developer who has built table-heavy admin interfaces or dynamic lists has likely used this.

TypeScript

TypeScript is the default in most frontend codebases in 2026. If your project uses it, test for it.

The most revealing question is about generics. “Write a function that takes an array of any type and returns a new array containing only the elements that satisfy a predicate.” A developer who understands generics writes:

function filter<T>(arr: T[], predicate: (item: T) => boolean): T[] {
  return arr.filter(predicate);
}

Someone who does not reaches for any. any in TypeScript is a code smell in a typed codebase, and a developer who defaults to it has not internalized why TypeScript is worth using.

Also ask about the difference between interface and type. Both can describe object shapes. interface can be extended and merged; type can describe unions, intersections, and mapped types. In practice the distinction is less important than understanding that they are not the same thing.

What the screen actually reveals

The framework question comes last, not first. By the time you reach it, you already know whether the candidate understands the platform. Someone strong on CSS, HTML, and JavaScript fundamentals who knows Vue but not React will be productive in a React codebase within a few weeks. Someone who knows React well but cannot explain specificity or LCP will hit the same walls repeatedly, regardless of which project they work on.

That is the screen we have found works. If you want to compare candidates against a consistent rubric, the what it costs to hire a developer post covers how to think about the total cost of a hire beyond the rate, including the real cost of screening time.

If you would rather skip the search, codercops screens React developers and hands you a vetted shortlist. See available React developers on codercops and post your role to get matched.