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Map.prototype.getOrInsert()

main Documentación oficial Licencia CC-BY-SA-2.5Descargado el 2026-08-02

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The getOrInsert() method of {{jsxref("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 {{jsxref("Map.prototype.getOrInsertComputed()")}} instead, which takes a callback to compute the default value only if it's actually needed.

{{InteractiveExample("JavaScript Demo: Map.prototype.getOrInsert()")}}

```js interactive-example const map = new Map([["bar", "foo"]]); console.log(map.getOrInsert("bar", "default")); // Expected output: "foo"

console.log(map.getOrInsert("baz", "default")); // Expected output: "default"

## Syntax

```js-nolint
getOrInsert(key, defaultValue)

Parameters#

  • key
  • : The key of the value to return from the Map object. Object keys are compared by reference, not by value.
  • defaultValue
  • : The value to insert and return if the key is not already present in the Map object.

Return value#

The value associated with the specified key in the Map object. If the key can't be found, defaultValue is inserted and returned.

Description#

The getOrInsert() method is equivalent to the following:

if (map.has(key)) {
  return map.get(key);
}
map.set(key, defaultValue);
return defaultValue;

It is also similar to the following pattern (which is slightly less reliable if null or undefined are valid values in your map):

map.set(key, map.get(key) ?? defaultValue);

Examples#

Multimap#

In a map where each key is mapped to an array of values, you can use getOrInsert() to ensure that the array exists for a given key before attempting to push a new value to the array.

map.getOrInsert(key, []).push(value);

Applying default values#

You can use getOrInsert() to ensure that a key exists in a map, even if you currently don't need its value. This is usually to normalize user input.

Imagine you have a map of user preferences, and you want to ensure that a certain preference is always set to a default value if the user hasn't specified it:

const options = readConfig();
options.getOrInsert("theme", "light");
options.getOrInsert("fontSize", 14);

// Later in your code, you can safely assume these options exist
document.body.dataset.theme = options.get("theme");

Specifications#

{{Specifications}}

Browser compatibility#

{{Compat}}

See also#