Quiz Entry - updated: 2026.07.14
What is the purpose of res.type() in Express?
res.type() sets the response's Content-Type header, telling the client how to interpret the data it receives.
// JSON data
res.type('application/json');
// HTML page
res.type('text/html');
// Plain text
res.type('text/plain');
Common content types:
| Type | Content-Type | Use |
|---|---|---|
| JSON | application/json |
APIs |
| HTML | text/html |
Web pages |
| Plain text | text/plain |
Simple text |
| CSS | text/css |
Stylesheets |
| JavaScript | application/javascript |
Scripts |
| Images | image/png, image/jpeg |
Images |
Why it matters:
- Browser decides how to display/process the response
- JSON response with wrong type may not parse correctly
- Security headers depend on content type
Shortcut: res.json() automatically sets application/json.