Truncate a number to decimal places without rounding

Cut the decimal representation after a number of digits.

JavaScript Version 1.0.0 · MIT · .md

function toFixedDown({ n, digits }) { return Number(`${n}`.match(new RegExp(`^-?\\d+(?:\\.\\d{0,${digits}})?`))[0]); }

Input & expected output

{
  "n": 25.198726354,
  "digits": 2
}

25.19

The edge case

{
  "n": -1.999,
  "digits": 1
}

-1.9

Know the limits

• Works on the decimal string, so floating-point drift does not round the result up.
• Numbers that print in exponent form, such as 1e-7, are outside this contract.

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.