Check if a string contains only letters

Test for one or more ASCII letters.

JavaScript Version 1.0.0 · MIT · .md

function isAlpha(text) { return /^[A-Z]+$/i.test(text); }

Input & expected output

"SMTP"

true

The edge case

"Café"

false

Know the limits

• ASCII only: use /^\p{L}+$/u for letters in any script.

The function above is the implementation used by the lab. The lab validates JSON types and caps size before execution; include equivalent validation when accepting untrusted input in your application.

Keep exploring

• Check whether all values are equal — Compare every item with the first using Object.is.
• Check whether an object is empty — Check for own enumerable string keys on a JSON object.
• Check whether an integer is even — Test parity for safe integers, including zero and negative values.