Effectively duplicates an async iterable into multiple async iterables. It guarantees that the async iterable source will be iterated in the same order in all the duplicated async iterables, and the source will be only iterated once.

import { tee } from "./tee.ts";

async function* source() {
  console.log("Yielding 1...");
  yield 1;
  console.log("Yielding 2...");
  yield 2;
  console.log("Yielding 3...");
  yield 3;
}

const [a, b, c] = tee(source(), 3);
for await (const value of a) console.log('a:', value);
for await (const value of b) console.log('b:', value);
for await (const value of c) console.log('c:', value);

The above example will print the following:

Yielding 1...
a: 1
Yielding 2...
a: 2
Yielding 3...
a: 3
b: 1
b: 2
b: 3
c: 1
c: 2
c: 3

Note that console.log() calls in the source function are executed only once, and not three times. Also these numbers are always in the same order.