Get the length of a string in bytes

Count UTF-8 bytes rather than characters.

JavaScript Version 1.0.0 · MIT · .md

function byteLength(text) { return new TextEncoder().encode(text).length; }

Input & expected output

"héllo"

6

The edge case

"😀"

4

Know the limits

• UTF-8 is what most APIs and email bodies use. Email header lines are limited to 998 bytes excluding CRLF (RFC 5322); measure bytes, not characters.
• The original used new Blob([text]).size, which also measures UTF-8.

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

• Capitalize a string — Uppercase the first Unicode code point and preserve the remaining text.
• Reverse a string — Reverse Unicode code points without splitting surrogate pairs.
• Check a palindrome — Compare a string with its code-point reversal.