isWeakMap()

isWeakMap(value): value is WeakMap<any, any>

Checks if value is a WeakMap.

DEPRECATED

Use instanceof WeakMap directly instead.

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Parameters

value: unknown

The value to check.

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Returns: value is WeakMap<any, any>

true if value is a WeakMap, else false.

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See Also

WeakMap - MDN

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Since

2.0.0

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Also known as

isWeakMap (Lodash, es-toolkit) · ❌ (Remeda, Radashi, Ramda, Effect, Modern Dash, Antfu)

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Example

// ❌ Deprecated approach
isWeakMap(new WeakMap());  // => true
isWeakMap(new Map());      // => false

// ✅ Recommended approach
new WeakMap() instanceof WeakMap;  // => true
new Map() instanceof WeakMap;      // => false

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How it works?

Checks if value is a WeakMap. Deprecated: Use instanceof WeakMap directly.

Native Equivalent

// ❌ isWeakMap(value)
// ✅ value instanceof WeakMap

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Use Cases

Check weak collection 📌

Check for weak collection types.

#WeakMap#WeakSet#check#collection

value instanceof WeakMap;
value instanceof WeakSet;

Validate collection type

Ensure correct collection type.

#validate#collection#type#weak

if (cache instanceof WeakMap) {
  return cache.get(key);
}

Type narrowing

TypeScript type guard.

#type#narrow#guard#instance

const isWeakMap = (v: unknown): v is WeakMap<object, unknown> =>
  v instanceof WeakMap;