Checks if value is classified as a WeakMap object. Part of Lodash Lang since 4.3.0 (stable — not deprecated).
Pass the value you want to inspect or convert. Read the return type carefully before you use the result.
Call _.isWeakMap. Start with this line.
_.isWeakMap(value)| Call | What it does |
|---|---|
_.isWeakMap(value) | Primary signature. |
Prefer import isWeakMap from "lodash/isWeakMap" when you want a smaller bundle.
_.isWeakMap(value)| Parameter | Description |
|---|---|
| value | Required. The value to check |
| Return Value | Description |
|---|---|
| * | true if WeakMap, else false |
new WeakMapA real WeakMap instance is classified as a WeakMap.
_.isWeakMap(new WeakMap);
// → truenew WeakMap (empty WeakMap).[object WeakMap].true — it is a WeakMap.new MapMap is a different built-in — not a WeakMap.
_.isWeakMap(new Map);
// → falsenew Map.[object Map].false._.isMap for Maps.Populated WeakMaps still pass — contents are irrelevant.
var key = {};
var wm = new WeakMap();
wm.set(key, "meta");
_.isWeakMap(wm);
// → true
_.isWeakMap(new WeakMap());
// → true_.isWeakMap(wm) looks at type, not entries.new WeakMap() also returns true.Objects and WeakMaps both store keys, but only WeakMap instances pass.
_.isWeakMap({ get: function () {}, set: function () {} }); // → false
_.isWeakMap(Object.create(null)); // → false
_.isWeakMap(new WeakMap()); // → trueget/set do not make a WeakMap.Object.create(null) also fails.new WeakMap() → true._.isPlainObject for {}.Other collections and nullish values are not WeakMaps.
_.isWeakMap(new WeakSet()); // → false
_.isWeakMap(new Set([1])); // → false
_.isWeakMap(null); // → false
_.isWeakMap(undefined); // → false_.isWeakSet._.isSet.null / undefined fail cleanly._.isWeakMap is a Lodash Lang helper (available since 4.3.0, stable in 4.x). It runs anywhere Lodash runs — modern browsers (via CDN or bundle) and Node.js / Bun / Deno with npm install lodash. The host must also provide the ES WeakMap built-in (all evergreen engines do).
Available in [email protected] full builds and the lodash/isWeakMap modular import. Works in evergreen browsers and current Node LTS when Lodash is installed.
Bottom line: Safe for production once Lodash is on the page or in your bundle. Prefer import isWeakMap from "lodash/isWeakMap" for smaller builds. Native alternative: value instanceof WeakMap (note iframe/realm caveats).
Check whether a value is classified as a WeakSet.
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