Express res.jsonp() Method
What you’ll learn
- How to return JSONP responses with
res.jsonp(). - How callback wrapping works using query parameters.
- How to customize the callback parameter name.
- When to prefer CORS + JSON over JSONP.
Syntax
javascript
res.jsonp(body)
res.status(200).jsonp(body)1
Return JSONP data for legacy client
javascript
app.get('/api/legacy-user', function (req, res) {
res.jsonp({ id: 1, name: 'Mari' });
});2
Customize callback query key
javascript
app.set('jsonp callback name', 'cb');
app.get('/api/legacy-stats', function (req, res) {
res.jsonp({ ok: true, visits: 1200 });
});3
Send error as JSONP with status
javascript
app.get('/api/legacy-orders/:id', function (req, res) {
if (!/^\d+$/.test(req.params.id)) {
return res.status(400).jsonp({ error: 'Invalid id' });
}
res.jsonp({ id: Number(req.params.id), status: 'queued' });
});⚠️ Common pitfalls
- Use JSONP only when required for legacy clients; prefer standard JSON APIs with CORS for modern apps.
- Do not send sensitive data over JSONP endpoints.
- Keep callback behavior predictable and avoid mixing JSON and JSONP semantics unintentionally.
❓ FAQ
It sends JSON data wrapped in a JavaScript callback function for JSONP-style responses.
res.json() returns plain JSON, while res.jsonp() may wrap the payload in a callback based on query parameter.
Mostly for legacy clients that need JSONP. Modern APIs usually use CORS with res.json().
Yes, Express supports changing it via app settings such as app.set('jsonp callback name', 'cb').
JSONP has limitations and risks; prefer CORS-based JSON APIs when possible.
Did you know?
res.jsonp() sends JSON wrapped in a callback function, enabling legacy cross-domain script-based consumption.
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