Prefix an integer with zeros

Pad a non-negative integer to a given width.

JavaScript Version 1.0.0 · MIT · .md

function prefixWithZeros({ n, length }) { return String(n).padStart(length, '0'); }

Input & expected output

{
  "n": 42,
  "length": 5
}

"00042"

The edge case

{
  "n": 12345,
  "length": 3
}

"12345"

Know the limits

• Longer numbers are never cut, as the edge case shows. The original toFixed variant broke for numbers with as many digits as the width.

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

• Clamp a number to a range — Keep a number inside an inclusive minimum and maximum.
• Round to a number of digits — Apply decimal scaling and JavaScript rounding for display-oriented values.
• Add an ordinal suffix to a number — Append st, nd, rd or th to a positive integer.