Get the first defined and non-null value

Return the first item that is neither null nor undefined.

JavaScript Version 1.0.0 · MIT · .md

function coalesce(values) { return values.find(item => item !== undefined && item !== null) ?? null; }

Input & expected output

[
  null,
  "",
  "fallback"
]

""

The edge case

[
  null,
  null
]

null

Know the limits

• 0 and "" count as defined, as the example shows — unlike ||. The ?? operator does the same for two values.
• The original took rest arguments; the lab passes one array.

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

• Convert Celsius to Fahrenheit — Apply the temperature conversion without rounding the result.
• Convert hex to RGB — Expand #rgb if needed and read the red, green and blue channels.
• Convert URL parameters to object — Read a query string into an object; repeated keys become arrays.