Map.prototype.getOrInsertComputed()

The getOrInsertComputed() 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 default value computed from a given callback, and returns the inserted value.

Use this method instead of {{jsxref("Map.prototype.getOrInsert()")}} when the default value is expensive to compute, and you want to avoid computing it unless it's actually needed.

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

``js interactive-example const map = new Map([["bar", "foo"]]); const defaultCreator = (key) =>default for ${key}`;

console.log(map.getOrInsertComputed("bar", defaultCreator)); // Expected output: "foo"

console.log(map.getOrInsertComputed("baz", defaultCreator)); // Expected output: "default for baz"

## Syntax

```js-nolint
getOrInsertComputed(key, callback)

Parameters#

• key
• : The key of the element to return from the Map object. Object keys are compared by reference, not by value.
• callback
• : A function that returns the value to insert and return if the key is not already present in the Map object. The function is called with the following argument:
  • key
  • : The same key that was passed to getOrInsertComputed().

Return value#

The value associated with the specified key in the Map object. If the key can't be found, the result of callback(key) is inserted and returned.

Exceptions#

• {{jsxref("TypeError")}}
• : Thrown if callback isn't callable.

Examples#

Avoiding unnecessary default computation#

When using {{jsxref("Map.prototype.getOrInsert()")}}, the default value is computed every time, even if it is not needed. With getOrInsertComputed(), the default value is only computed when necessary.

const map = new Map([["bar", "foo"]]);
const defaultCreator = (key) => {
  console.log(`Creating default for ${key}`);
  return `default for ${key}`;
};

map.getOrInsert("bar", defaultCreator("bar")); // Logs "Creating default for bar"
map.getOrInsertComputed("bar", defaultCreator); // No log

Specifications#

{{Specifications}}

Browser compatibility#

{{Compat}}

See also#

• Polyfill of Map.prototype.getOrInsertComputed in core-js
• es-shims polyfill of Map.prototype.getOrInsertComputed
• {{jsxref("Map")}}
• {{jsxref("Map.prototype.get()")}}
• {{jsxref("Map.prototype.set()")}}
• {{jsxref("Map.prototype.has()")}}
• {{jsxref("Map.prototype.getOrInsert()")}}