JavaScript Map Reference
A Map holds key-value pairs where the keys can be any datatype.
A Map remembers the original insertion order of the keys.
Example
// Create a Map
const fruits = new Map([
["apples", 500],
["bananas", 300],
["oranges", 200]
]);
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Map Methods and Properties
| Method | Description |
|---|---|
| new Map() | Creates a new Map object |
| clear() | Removes all the elements from a Map |
| delete() | Removes a Map element specified by a key |
| entries() | Returns an iterator object with the [key, value] pairs in a Map |
| forEach() | Invokes a callback for each key/value pair in a Map |
| get() | Gets the value for a key in a Map |
| groupBy() | Groups object elements according to returned callback values |
| has() | Returns true if a key exists in a Map |
| keys() | Returns an iterator object with the keys in a Map |
| set() | Sets the value for a key in a Map |
| size | Returns the number of Map elements |
| values() | Returns an iterator object of the values in a Map |
You can add elements to a map with the set() method:
Example
// Create a Map
const fruits = new Map();
// Set Map Values
fruits.set("apples", 500);
fruits.set("bananas", 300);
fruits.set("oranges", 200);
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You can get elements from a map with the get() method:
JavaScript Objects vs Maps
Differences between JavaScript Objects and Maps:
| Object | Map |
|---|---|
| Not directly iterable | Directly iterable |
| Do not have a size property | Have a size property |
| Keys must be Strings (or Symbols) | Keys can be any datatype |
| Keys are not well ordered | Keys are ordered by insertion |
| Have default keys | Do not have default keys |
