Writing JSX in code
function Card() {
return (
<>
<h2>Ticket</h2>
<p>Open</p>
</>
);
}Read the example from data and control flow to the resulting UI. Keep the component boundary small.
Back to week 1
Topic
Writing JSX
Definition
JSX is a JavaScript syntax extension that compiles into React element descriptions.
In simpler words
JSX looks like HTML, but it follows JavaScript rules and describes what React should render.
Single roots, fragments, attributes, and self-closing elements.
After this you can
- Write valid JSX without common parser errors.
- Explain the trade-off to a teammate using a small example.
- Name at least one common bug pattern for this topic.
Understand Writing JSX
Single roots, fragments, attributes, and self-closing elements.
Start by identifying which value or browser behavior changes. Then describe the UI from that current input instead of editing the DOM as a separate source of truth.
Apply Writing JSX
Keep rendering as a calculation. Put user-triggered changes in event handlers, preserve UI memory in state, and reserve external synchronization for Effects or the server-state layer.
Name values by their UI meaning, test the loading and error path when data is remote, and avoid keeping two editable copies of the same value.
Ask before adding code: is this local UI memory, shared client state, or Nest-owned server state?
Where bugs hide
Definition
High-bug areas are places where a small API misuse looks correct but produces stale UI, duplicate work, or silent failures.
In simpler words
Each mistake below shows Wrong vs Right code — compare them side by side.
When something misbehaves, match the symptom to a pattern below before rewriting the feature.
Prefer fixing the ownership or update path over adding another Effect or sync step.
Mistake: Adjacent JSX roots
// Wrong
return (
<h1>Title</h1>
<p>Body</p>
);
// Right
return (
<>
<h1>Title</h1>
<p>Body</p>
</>
);Wrap siblings in a parent or fragment.
Mistake: class instead of className
// Wrong
<div class="card">
// Right
<div className="card">class is reserved in JavaScript.
Mistake: Unclosed void tag
// Wrong
return <input value={title}>;
// Right
return <input value={title} />;JSX requires self-closing tags for void elements.
Live playground
Writing JSX sandbox
Change one input at a time and predict the next render.
JSX describes UI. Toggle pieces and watch one tree update — that is declarative markup, not manual DOM edits.
Ticket
Open
return (
<>
<h2 className="card">Ticket</h2>
<p>Open</p>
</>
);Keep in mind
- Keep the formal definition in mind; it explains which tool belongs where.
- Prefer one source of truth over synchronized copies of the same value.
- When behavior surprises you, trace: input → update → render → committed UI.
- Study the Wrong vs Right examples in “Where bugs hide” before you merge.
Test
Check your understanding
At least 10 questions — mix of concept, syntax, practical, and logic. Score ≥ 80% (enforced by the API) to save progress.
Checking your session…
10 questions · concept 3 · syntax 3 · practical 2 · logic 2