.forEach already has this ability:
const someArray = [9, 2, 5];
someArray.forEach((value, index) => {
console.log(index); // 0, 1, 2
console.log(value); // 9, 2, 5
});
But if you want the abilities of for...of, then you can map the array to the index and value:
for (const { index, value } of someArray.map((value, index) => ({ index, value }))) {
console.log(index); // 0, 1, 2
console.log(value); // 9, 2, 5
}
That's a little long, so it may help to put it in a reusable function:
function toEntries<T>(a: T[]) {
return a.map((value, index) => [index, value] as const);
}
for (const [index, value] of toEntries(someArray)) {
// ..etc..
}
Iterable Version
This will work when targeting ES3 or ES5 if you compile with the --downlevelIteration compiler option.
function* toEntries<T>(values: T[] | IterableIterator<T>) {
let index = 0;
for (const value of values) {
yield [index, value] as const;
index++;
}
}
Array.prototype.entries() - ES6+
If you are able to target ES6+ environments then you can use the .entries() method as outlined in Arnavion's answer.