isArray()

isArray<T>(value): value is T[]

Checks if a value is an array.

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Type Parameters

T: T

The expected element type of the array.

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Parameters

value: unknown

The value to check.

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Returns: value is T[]

true if the value is an array, false otherwise.

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Since

2.0.0

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Example

isArray([1, 2, 3]); // => true
isArray('hello');   // => false

// Use instead
Array.isArray([1, 2, 3]); // => true

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How it works?

Type guard that checks if a value is an array.

Type Narrowing

Common Checks

Value	Result
[1, 2, 3]	true
[]	true
'hello'	false
{ length: 3 }	false
new Set([1, 2])	false

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Use Cases

Validate list structures 📌

Ensure a value is an array before iterating or mapping. Essential for processing API responses that might return single objects or arrays.

#validate#array#list#type-check#guard#iteration

if (isArray(data)) {
  data.forEach(item => process(item));
}

Normalize API responses 📌

Handle endpoints that return either a single item or an array. Essential for APIs with inconsistent response formats.

#normalize#API#responses#inconsistent#format#handling

const users = isArray(response.data) 
  ? response.data 
  : [response.data];

// Now always an array
users.forEach(user => processUser(user));

Type narrowing in conditionals

Safely access array methods after type check.

#narrowing#TypeScript#conditionals#safety#types#inference

function getFirst<T>(value: T | T[]): T | undefined {
  if (isArray(value)) {
    return value[0]; // TypeScript knows it's T[]
  }
  return value;
}