You might have stumbled upon the weird @@thingies
in JavaScript before. Maybe you saw an @@iterator
or an @@match
somewhere
These aren't valid JavaScript (@@iterator
would throw an error). They are actually internal Symbols used in
JavaScript. They are used to implement features like iteration, instanceOf
, and such internally. They actually might get removed or changed
For example: you can set @@isConcatSpreadable
to stop .concat
from spreading arrays.
const customArray = [1, 2, 3];
customArray[Symbol.isConcatSpreadable] = false;
const concatenatedArray = [4, 5, 6].concat(customArray);
console.log(concatenatedArray); // Output: [4, 5, 6, [1, 2, 3]]
Another one, a more useful one, is @@iterator
it is used internally to define iteration - ie in for loops.
const customIterable = {
[Symbol.iterator]() {
return {
next() {
// Infinite loop
return { value: 'anything', done: false }
// return {done: true} when done
}
}
}
}
for (const item of customIterable) {
console.log(item);
}
@@match
can also have potential use cases:
class CustomDateMatcher {
[Symbol.match](str) {
// ...logic...
}
}
const str = '21st of March';
console.log(str.match(new CustomDateMatcher('21/03'))); // Custom pattern matching result
More notable mentions:
-
@@toStringTag
for converting an object to a string -
@@toPrimitive
for converting an object to a primitive -
@@search
for.search()
- Full list on MDN
Do you have any ideas / suggestions for how to make use of this in code? Leave a comment!
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