Newly available Helpful for caches, grouping logic, and memoization where default creation is a repeated pattern.

Map getOrInsert()

The getOrInsert() method of Map instances returns the value corresponding to the specified key in this Map. If the key is not present, it inserts a new entry with the key and a given default value, and returns the inserted value.

If the computation of the default value is expensive, consider using Map.prototype.getOrInsertComputed() instead, which takes a callback to compute the default value only if it's actually needed.

MapCachingInitialization

Browser support

Feature Desktop Mobile
Chrome
Edge
Firefox
Safari
Chrome Android
Safari iOS
javascript.builtins.Map.getOrInsert
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Built-in object
Map.getOrInsertComputed

The getOrInsertComputed() method of Map instances returns the value corresponding to the specified key in this Map. If the key is not present, it inserts a new entry with the key and a default value computed from a given callback, and returns the inserted value.
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WeakMap.getOrInsert

The getOrInsert() method of WeakMap instances returns the value corresponding to the specified key in this WeakMap. If the key is not present, it inserts a new entry with the key and a given default value, and returns the inserted value.
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WeakMap.getOrInsertComputed

The getOrInsertComputed() method of WeakMap instances returns the value corresponding to the specified key in this WeakMap. If the key is not present, it inserts a new entry with the key and a default value computed from a given callback, and returns the inserted value.
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1+Supported (version) Not supported ※Has note Sub-feature descriptions sourced from MDN Web Docs (CC BY-SA 2.5)

Syntax

JAVASCRIPT 
const map = new Map();

map.getOrInsert('key', 'default');
// If 'key' is not in the map, set it to 'default' and return it

Live demo

Get or insert into a Map

Use the proposal if available, otherwise fall back to a helper.

JavaScript
Output
Press the Run button

Build grouped buckets

Create arrays on demand when grouping records into a Map.

JavaScript
Output
Press the Run button

Reuse existing entries

Confirm that the same key does not recreate the stored value.

JavaScript
Output
Press the Run button

Use cases

  • Bucket creation

    Initialize arrays, sets, or counters in a map only when a key appears for the first time.

  • Memoized storage

    Create and retain derived values lazily without writing repetitive key-exists checks.

Cautions

  • Use a clear default creation strategy so inserted values remain predictable and side effects stay obvious.
  • If the initialization step is expensive or async, make the lifecycle explicit instead of hiding too much in one call.

Accessibility

  • This feature affects data organization rather than UI directly.
  • Cleaner state initialization can still reduce bugs in user-facing collections and lists.

Related links