The yield*
is used to delegate to another generator
or iterable object.
yield* expression;
expression
The yield*
expression iterates over the operand and yield
s each value returned by it.
The value of yield*
expression itself is the value returned by that iterator when it's closed (i.e., when done
is true
).
In following code, values yielded by g1()
are returned from next()
calls just like those which are yielded by g2()
.
function* g1() { yield 2; yield 3; yield 4; } function* g2() { yield 1; yield* g1(); yield 5; } const iterator = g2(); console.log(iterator.next()); // {value: 1, done: false} console.log(iterator.next()); // {value: 2, done: false} console.log(iterator.next()); // {value: 3, done: false} console.log(iterator.next()); // {value: 4, done: false} console.log(iterator.next()); // {value: 5, done: false} console.log(iterator.next()); // {value: undefined, done: true}
Besides generator objects, yield*
can also yield
other kinds of iterables (e.g., arrays, strings, or arguments
objects).
function* g3() { yield* [1, 2]; yield* '34'; yield* Array.from(arguments); } const iterator = g3(5, 6); console.log(iterator.next()); // {value: 1, done: false} console.log(iterator.next()); // {value: 2, done: false} console.log(iterator.next()); // {value: "3", done: false} console.log(iterator.next()); // {value: "4", done: false} console.log(iterator.next()); // {value: 5, done: false} console.log(iterator.next()); // {value: 6, done: false} console.log(iterator.next()); // {value: undefined, done: true}
yield*
expression itselfyield*
is an expression, not a statement—so it evaluates to a value.
function* g4() { yield* [1, 2, 3]; return 'foo'; } function* g5() { const g4ReturnValue = yield* g4(); console.log(g4ReturnValue) // 'foo' return g4ReturnValue; } const iterator = g5(); console.log(iterator.next()); // {value: 1, done: false} console.log(iterator.next()); // {value: 2, done: false} console.log(iterator.next()); // {value: 3, done: false} done is false because g5 generator isn't finished, only g4 console.log(iterator.next()); // {value: 'foo', done: true}
Desktop | ||||||
---|---|---|---|---|---|---|
yield* |
39 | 12 | 27
|
No | 26 | 10 |
Mobile | ||||||
---|---|---|---|---|---|---|
yield* |
39 | 39 | 27
|
26 | 10 | 4.0 |
Server | |
---|---|
yield* |
4.0.0
|
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Licensed under the Creative Commons Attribution-ShareAlike License v2.5 or later.
https://wiki.developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/yield*