while While loop
Last updated: 2026-09-09
while While loop
while repeats while the condition is true — for unknown iteration counts.
| Category | Statements |
|---|---|
| ES version | ES1 |
📝 Syntax
while (condition) { ... }Returns：undefined.
Mutates the original：No (returns a new value)
▶ Example
Edit the code, press Run, and see the result in the output panel:
Output：
3
2
1
a
b
c⚠️ Warning Forgetting to update the condition causes an infinite loop.
💡 Tip do...while runs at least once; while may run zero times.
🌐 Browser support
| Browser |  Chrome |
 Edge |
 Firefox |
 Safari |
 Opera |
|---|---|---|---|---|---|
| while | ✓ 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
Qwhile vs do...while?
Awhile checks first (may skip); do...while runs at least once.
Qwhile or for?
Afor for counted loops; while for condition-only.
QHow to avoid infinite loops?
AMake sure the condition variable is updated inside the loop.
