The double at sign (@@
) is used for referring to a "well-known symbol" — which are built-in symbols. However, the double at sign itself is not a valid JavaScript syntax.
Following is a list of some well-known symbols in JavaScript:
For example, you can implement [@@iterator]
(or Symbol.iterator
) as a generator method, to make a class object iterable:
// ES6+ class Foo { *[Symbol.iterator]() { yield 1; yield 2; yield 3; } } const foo = new Foo(); for (const val of foo) { console.log(val); // 1 2 3 } console.log([ ...foo ]); // [1, 2, 3]
The same can be implemented in an object literal, for example, like so:
// ES6+ const obj = { [Symbol.iterator]: function* () { yield 1; yield 2; yield 3; }, }; for (const val of obj) { console.log(val); // 1 2 3 } console.log([ ...obj ]); // [1, 2, 3]
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