String.toLowerCase() Convert to lowercase
Last updated: 2026-09-09
String.toLowerCase() Convert to lowercase
toLowerCase returns a new lowercased string. The standard method for case-insensitive comparisons.
| Category | Strings |
|---|---|
| ES version | ES1 |
📝 Syntax
const lower = str.toLowerCase();Returns：A new lowercased string.
Mutates the original：No (returns a new value)
▶ Example
Edit the code, press Run, and see the result in the output panel:
Output：
false
true💡 Tip Case-insensitive compare: lowercase both sides.
ℹ️ info toLocaleLowerCase() follows locale rules.
🌐 Browser support
| Browser |  Chrome |
 Edge |
 Firefox |
 Safari |
 Opera |
|---|---|---|---|---|---|
| String.toLowerCase() | ✓ 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 toLowerCase mutate the original?
ANo — it returns a new string. All JS strings are immutable.
QWhy lowercase both sides?
ALowering only one side makes the comparison wrong — both must match format.
QDoes toLowerCase affect Chinese?
AChinese has no case — the call is a harmless no-op; only cased scripts change.
