Prepend a line number to each line of a text document

Number lines from 1, right-aligned to two characters.

JavaScript Version 1.0.0 · MIT · .md

function prependNumbers(text) { return text.split(/\r?\n/).map((line, i) => `${String(i + 1).padStart(2, ' ')} ${line}`).join('\n'); }

Input & expected output

"alpha\nbeta"

" 1 alpha\n 2 beta"

The edge case

""

" 1 "

Know the limits

• Numbers above 99 widen the gutter. An empty text is one empty line.

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.