isNil()

isNil(value): value is null | undefined

Checks if a value is null or undefined.

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Parameters

value: unknown

The value to check.

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Returns: value is null | undefined

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

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See Also

• isNull
• isUndefined

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Since

2.0.0

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Example

isNil(null);      // => true
isNil(undefined); // => true
isNil(0);         // => false
isNil('');        // => false
isNil(false);     // => false

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How it works?

Type guard that checks if a value is null or undefined.

Narrowing

Falsy vs Nil

Value	isNil	value
null	true	true
undefined	true	true
0	false	true
''	false	true
false	false	true

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Use Cases

Check for nullish values 📌

Check if a value is null or undefined. Essential for defensive programming and optional value handling.

#check#null#undefined#nullish#optional#defensive

if (isNil(value)) {
  return defaultValue;
}

Early return for missing data

Guard clauses to exit early when required data is missing.

#early-return#missing#guard#validation#safety#defensive

function processUser(user: User | null | undefined) {
  if (isNil(user)) {
    return { error: "User not found" };
  }
  
  // TypeScript knows user is User here
  return { name: user.name, email: user.email };
}