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@rauschma
Last active April 8, 2018 02:25
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// Lazy (=on-demand) zip()
for (const [i, x] of zip(naturalNumbers(), naturalNumbers())) {
console.log(i, x);
if (i >= 2) break;
}
// Output:
// 0 0
// 1 1
// 2 2
// Eager Array.from() (.entries() is lazy)
for (const [i, x] of Array.from(naturalNumbers()).entries()) {
console.log(i, x);
if (i >= 2) break;
}
// Infinite loop
function* naturalNumbers() {
for (let n=0;; n++) {
yield n;
}
}
function zip(...iterables) {
const iterators = iterables.map(i => i[Symbol.iterator]());
let done = false;
return {
[Symbol.iterator]() {
return this;
},
next() {
if (!done) {
const items = iterators.map(i => i.next());
done = items.some(item => item.done);
if (!done) {
return { value: items.map(i => i.value) };
}
// Done for the first time: close all iterators
for (const iterator of iterators) {
if (typeof iterator.return === 'function') {
iterator.return();
}
}
}
// We are done
return { done: true };
}
}
}
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