javascript Map Set WeakMap WeakSet

Posted 2021-05-03

/* Sets 
   Store unique values of any type,
*/
var s = new Set();
s.add("hello").add("goodbye").add("hello");
s.size === 2;
s.has("hello") === true;

/* Maps
   key-value pairs and remembers the original
   insertion order of the keys
*/
var m = new Map();
m.set("hello", 42);
m.set(s, 34);
m.get(s) == 34;

/*  Weak Maps
    keys are weakly referenced
    keys must be objects and 
    the values can be arbitrary values
*/
var wm = new WeakMap();
wm.set(s, { extra: 42 });
wm.size === undefined

/* Weak Sets
Store weakly held objects in a collection */
var ws = new WeakSet();
ws.add({ data: 42 });