Map and set in JavaScript

The default object representation of JavaScript {} can be thought of as a map or dictionary data structure in other languages, a set of key-value pairs.

But the JavaScript object has a small problem, that is, the key must be a string , but actually number or other data type as a key is also very reasonable.

Map is the structure of a set of key-value pairs with extremely fast lookup speeds.

var m  new Map ([[' Michael ', 95],[' Bob ', 75],[' Tracy ', []]);        M.get (' Michael '); //  the

Initializing a map requires a two-dimensional array, or directly initializing an empty map. Map has the following methods:

        var New Map (); // Empty map        M.set (' Adam ', 67); // Add a new Key-value        M.set (' Bob ',);        M.has (' Adam '); // is there a key ' Adam ': true        M.get (' Adam '); //  the        M.delete(' Adam '); // Delete key ' Adam '        M.get (' Adam '); // undefined

There is rain a key can only correspond to one value, so, multiple times to a key put value, the following value will overwrite the front

var New Map ();        M.set (' Adam ', ();        M.set (' Adam ',N);        M.get (' Adam '); //  the

Set

Set is similar to a map, but it is also a set of keys, but does not store value, because key cannot be duplicated, so there is no duplicate key in set.

To create a set, you need to provide an array as input, or create an empty set directly:

var New Set (); // Empty Set        var New Set ([n/a]); // contains

Repeating elements are automatically filtered in set:

var New Set ([1,2,3,3, ' 3 ']); s; // set{1,2,3, ' 3 '}, filters out a repeating element 3

You can add elements to the set by using the Add (key) method, but you can add them repeatedly, but it won't work.

>>> S.add (4)        >>>s        {1,2,3,4}        >>> s.add (4)         >>> s        {1,2,3,4}

You can delete an element by using the Delete (key) method:

var New Set ([n/a]);        s; // set{1,2,3}        S.Delete(3);        s; // set{1,2}

Map and set in JavaScript