# Map

A Map object holds key-value pairs, where any value (both objects and primitive values) may be used as either a key or a value. Insertion order is remembered, which allows iteration in that order.

### set(key, value) <sub>function</sub>

Add or update an entry in the Map with the specified key and value.



**key**: The key of the element to add or update.

**value**: The value associated with the key.


**Returns**: The Map object (for chaining).


### get(key) <sub>function</sub>

Return the value associated with the specified key, or undefined if no
such key exists.



**key**: The key of the element to retrieve.


**Returns**: The value associated with the key, or undefined if not found.


### has(key) <sub>function</sub>

Return a boolean indicating whether the Map contains an element with the
specified key.



**key**: The key to test for presence in the Map.


**Returns**: True if the key is found, otherwise false.


### delete(key) <sub>function</sub>

Remove the specified key and its associated value from the Map, if it exists.



**key**: The key to remove.


**Returns**: True if an element was removed, otherwise false.


### clear() <sub>function</sub>

Remove all entries from the Map, leaving it empty.



**Returns**: None


### size <sub>accessor</sub>

(read only)

A read-only property returning the number of key-value pairs in the Map.



**Returns**: The number of entries in the Map.


### forEach(callbackFn, thisArg) <sub>function</sub>

Execute a provided callback function once per each key-value pair in the Map,
in insertion order.



**callbackFn**: A function(value, key, map) to execute on each entry.

**thisArg**: Optional. A value to use as 'this' when executing callbackFn.


**Returns**: None


### values() <sub>function</sub>

Return a new Iterator object that contains the values for each element
in the Map, in insertion order.



**Returns**: An iterator of the Map's values.


### keys() <sub>function</sub>

Return a new Iterator object that contains the keys for each element in
the Map, in insertion order.



**Returns**: An iterator of the Map's keys.


### entries() <sub>function</sub>

Return a new Iterator object that contains the [key, value] pairs for
each element in the Map, in insertion order.



**Returns**: An iterator of [key, value] pairs.