Yield Many With yield*
Version: ES2015
Level: Intermediate
When you yield a value from a generator with yield it provides that value as an iteration value when the generator object iterator is used in iteration. When yielding multiple values, you might consider handling this through a loop.
function * gen () {
let nums = [1, 2, 3];
for (let num of nums) {
yield num;
}
}
for (let value of gen()) {
console.log(value);
}
/* logs:
1
2
3
*/
If you’re looping through an iterable this way, you can automatically yield every value in that iterator using yield*. yield* is a shortcut that will automatically take the values of an iterable and yield them out individually from the current generator function.
function * gen () {
let nums = [1, 2, 3];
yield * nums;
}
for (let value of gen()) {
console.log(value);
}
/* logs:
1
2
3
*/
Note that if you were try to yield an iterable without the *, you’d get the entire iterable in the iteration rather than its individual values.
function * gen () {
let nums = [1, 2, 3];
yield nums;
}
for (let value of gen()) {
console.log(value);
}
/* logs:
[1, 2, 3]
*/
The use of yield* instead lets you spread out the iterable between multiple iterations, not unlike using the spread operator (...) in arrays or argument lists.
More info:
