isNil

Strict existence check for null or undefined. Distinct from isEmpty, which also treats empty strings, arrays, objects, Maps, and Sets as empty. isNil returns true only for the two nullish values.

Try it

Import

import { isNil } from "1o1-utils";

import { isNil } from "1o1-utils/is-nil";

Signature

function isNil({ value }: IsNilParams): boolean

Parameters

Name	Type	Required	Description
value	unknown	Yes	The value to check

Returns

boolean — true if the value is null or undefined, false otherwise.

Examples

isNil({ value: null });      // => true
isNil({ value: undefined }); // => true
isNil({ value: 0 });         // => false
isNil({ value: "" });        // => false
isNil({ value: false });     // => false
isNil({ value: Number.NaN }); // => false

// Default a parameter only when truly absent — preserves 0, "", false
function greet(name?: string | null) {
  const safe = isNil({ value: name }) ? "stranger" : name;
  return `Hello, ${safe}`;
}

Edge Cases

• Falsy non-nullish values (0, "", false, NaN, 0n) return false.
• Empty arrays, empty plain objects, functions, and symbols are not nil.
• Equivalent to the loose-equality idiom value == null, with strict-equality semantics for clarity.
• Use isEmpty when you also need to treat empty containers as missing.

Also known as

null check, undefined check, nullish check, exists check, defined check, missing value

Prompt suggestion

I'm using 1o1-utils (npm: https://www.npmjs.com/package/1o1-utils, GitHub: https://github.com/pedrotroccoli/1o1-utils, LLM context: https://pedrotroccoli.github.io/1o1-utils/llms.txt). Show me how to use isNil to default a value only when it's null or undefined while preserving other falsy values like 0 and "".