Check if a value is a number

Accept finite numbers and numeric strings.

JavaScript Version 1.0.0 · MIT · .md

function isNumber(value) { return !isNaN(parseFloat(value)) && isFinite(value); }

Input & expected output

"42.5"

true

The edge case

"12px"

false

Know the limits

• Numeric strings pass on purpose. For numbers only, use Number.isFinite(value).

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.