Baseline Widely available
The add() method of WeakSet instances appends a new object to the end of this WeakSet.
const weakset1 = new WeakSet();
const object1 = {};
weakset1.add(object1);
console.log(weakset1.has(object1));
// Expected output: true
try {
weakset1.add(1);
} catch (error) {
console.log(error);
// Expected output (Chrome): TypeError: Invalid value used in weak set
// Expected output (Firefox): TypeError: WeakSet value must be an object, got 1
// Expected output (Safari): TypeError: Attempted to add a non-object key to a WeakSet
}
value
Must be either an object or a non-registered symbol. The value to add to the WeakSet collection.
The WeakSet object.
TypeError
Thrown if value is not an object or a non-registered symbol.
const ws = new WeakSet();
ws.add(window); // add the window object to the WeakSet
ws.has(window); // true
// WeakSet only takes objects as arguments
ws.add(1);
// results in "TypeError: Invalid value used in weak set" in Chrome
// and "TypeError: 1 is not a non-null object" in Firefox
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