String.toUpperCase() Convert to uppercase
Last updated: 2026-09-09
String.toUpperCase() Convert to uppercase
toUpperCase returns a new uppercased string. Used for title formatting, constant generation and case-insensitive keys.
| Category | Strings |
|---|---|
| ES version | ES1 |
📝 Syntax
const upper = str.toUpperCase();Returns：A new uppercased string.
Mutates the original：No (returns a new value)
▶ Example
Edit the code, press Run, and see the result in the output panel:
Output：
DEVELOPMENT
Javascript💡 Tip Title-case: str.split(' ').map(w => w[0].toUpperCase() + w.slice(1)).join(' ').
ℹ️ info toUpperCase and toLowerCase are a pair.
🌐 Browser support
| Browser |  Chrome |
 Edge |
 Firefox |
 Safari |
 Opera |
|---|---|---|---|---|---|
| String.toUpperCase() | ✓ v1 | ✓ v12 | ✓ v1 | ✓ v1 | ✓ v1 |
| Supported by all modern browsers | |||||
🏷️ Related Items
💡 Related Cases
More case studies coming soon — check back later.
📚 Related Tutorials
❓ FAQ
QDoes toUpperCase mutate the original?
ANo — it returns a new string; the original is unchanged.
QHow to title-case every word?
Astr.toLowerCase().split(' ').map(w => w.charAt(0).toUpperCase() + w.slice(1)).join(' ').
QDoes it affect digits and symbols?
ANo — digits, punctuation and Chinese have no case and pass through unchanged.
