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Concept visual
Start at both ends
WeakSet is a collection of values where the values must be objects. A WeakSet holds weak references to its values.
// Create a WeakSet let mySet = new WeakSet();
// Create an Object let myObj = {fname:"John", lname:"Doe"};
// Add the Object mySet.add(myObj);// Do I have myObj in the mySet?
let answer = mySet.has(myObj);
// Create a WeakSet let mySet = new WeakSet();
// Create an Object let myObj = {fname:"John", lname:"Doe"};
// Add the Object mySet.add(myObj);
// Delete the Object mySet.delete(myObj);// Do I have myObj in the mySet?
let answer = mySet.has(myObj);JavaScript employs a memory management mechanism known as Garbage Collection.
Reclaim memory occupied by variables that are no longer in use
Unlike a regular Set, a WeakSet does not prevent its values from being garbage collected. If a value (an object) has no references in a program, it becomes eligible for garbage collection. When the value is garbage collected, its is removed from the WeakSet.
// Create a WeakSet let mySet = new WeakSet();
// Create an Object let myObj = {fname:"John", lname:"Doe"};
// Add the Object mySet.add(myObj);
// Remove the Object from memory myObj = null;// Now myObj in mySet will be garbage collected
Primitive values cannot be values in a WeakSet. The values must be objects.
This restriction is tied to the garbage collection mechanism;primitives are not garbage collected in the same way as objects.
A WeakSet is similar to a Set, but it only stores objects, and holds them weakly. If there are no other references to an object, it gets garbage collected automatically. This makes it handy for tracking objects without storing extra data (like counts).
let text = "";
// Create a WeakSet to track persons const persons = new WeakSet();
// Visitor Objects const John = {name:"John", age:40};
const Paul = {name:"Paul", age:41};
const Ringo = {name:"Ringo", age:42};
const George = {name:"George", age:43};
// Track visits track(Paul);
track(Ringo);
track(Paul);
// Function to track visitors function track(visitor) {
if (persons.has(visitor)) {
text += visitor.name + " is visiting again.<br>";
} else {
persons.add(visitor);
text += visitor.name + ", age" + visitor.age +", is visiting for the first time<br>";
}
}If you want to count the visits as well: Try to use a WeakMap instead.
If you remove all references to a visitor object:
John = null;
// The entry for John is now removed from the WeakMap (persons)WeakSets are not enumerable. You cannot iterate over the values with for loops, forEach(), or values(). You cannot access the size. WeakSets have no size property.
Formula
A WeakSet is minimal, memory - safe, and purpose - built for tracking objects privately and efficiently.WeakSet provides a limited set of methods: new WeakSet()
Returns true if an object exists in a WeakSet
A spread operator (...)
Any logic methods (union, difference, intersection) Any iteration methods (forEach, keys, values, entries) The above is by design: Objects may disappear in garbage collection, it makes no sense to iterate over or count them.