This content originally appeared on DEV Community and was authored by Clean Code Studio
JavaScript / WeakSet — DevDocs
WeakSet
The WeakSet object lets you store weakly held objects in a collection.
Description
WeakSet objects are collections of objects. Just as with Sets, each object in a WeakSet may occur only once; all objects in a WeakSet's collection are unique.
The main differences to the Set object are:
-
WeakSets are collections of objects only. They cannot contain arbitrary values of any type, asSets can. -
The
WeakSetis weak, meaning references to objects in aWeakSetare held weakly. If no other references to an object stored in theWeakSetexist, those objects can be garbage collected.Note: This also means that there is no list of current objects stored in the collection.
WeakSetsare not enumerable.
Use case: Detecting circular references
Functions that call themselves recursively need a way of guarding against circular data structures by tracking which objects have already been processed.
WeakSets are ideal for this purpose:
// Execute a callback on everything stored inside an object
function execRecursively(fn, subject, \_refs \= null){
if(!\_refs)
\_refs \= new WeakSet();
// Avoid infinite recursion
if(\_refs.has(subject))
return;
fn(subject);
if("object" \=== typeof subject){
\_refs.add(subject);
for(let key in subject)
execRecursively(fn, subject\[key\], \_refs);
}
}
const foo \= {
foo: "Foo",
bar: {
bar: "Bar"
}
};
foo.bar.baz \= foo; // Circular reference!
execRecursively(obj \=> console.log(obj), foo);
Here, a WeakSet is created on the first run, and passed along with every subsequent function call (using the internal _refs parameter).
The number of objects or their traversal order is immaterial, so a WeakSet is more suitable (and performant) than a Set for tracking object references, especially if a very large number of objects is involved.
Constructor
Creates a new WeakSet object.
Instance methods
Appends value to the WeakSet object.
WeakSet.prototype.delete(value)
Removes value from the WeakSet. WeakSet.prototype.has(value) will return false afterwards.
Returns a boolean asserting whether value is present in the WeakSet object or not.
Examples
Using the WeakSet object
const ws \= new WeakSet();
const foo \= {};
const bar \= {};
ws.add(foo);
ws.add(bar);
ws.has(foo); // true
ws.has(bar); // true
ws.delete(foo); // removes foo from the set
ws.has(foo); // false, foo has been removed
ws.has(bar); // true, bar is retained
Note that foo !== bar. While they are similar objects, they are not the same object. And so they are both added to the set.
This content originally appeared on DEV Community and was authored by Clean Code Studio
Clean Code Studio | Sciencx (2021-08-16T05:42:54+00:00) JavaScript Weak Set (Dev Docs Breakdown). Retrieved from https://www.scien.cx/2021/08/16/javascript-weak-set-dev-docs-breakdown/
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