語法
js
next()
next(value)
引數
value可選-
一個可選值，用於修改生成器的內部狀態。傳遞給
next()方法的值將由yield接收。
返回值
示例
使用 next()
以下示例展示了一個生成器以及 next 方法返回的物件。
js
// An async task. Pretend it's doing something more useful
// in practice.
function delayedValue(time, value) {
return new Promise((resolve, reject) => {
setTimeout(() => resolve(value), time);
});
}
async function* createAsyncGenerator() {
yield delayedValue(500, 1);
yield delayedValue(500, 2);
yield delayedValue(500, 3);
}
const asyncGen = createAsyncGenerator();
asyncGen.next().then((res) => console.log(res)); // { value: 1, done: false }
asyncGen.next().then((res) => console.log(res)); // { value: 2, done: false }
asyncGen.next().then((res) => console.log(res)); // { value: 3, done: false }
asyncGen.next().then((res) => console.log(res)); // { value: undefined, done: true }
向生成器傳送值
在此示例中，next 是帶值呼叫的。
注意： 第一次呼叫不會輸出任何內容，因為生成器最初沒有產生任何值。
js
// An async task. Pretend it's doing something more useful
// in practice.
function sleep(time) {
return new Promise((resolve, reject) => {
setTimeout(resolve, time);
});
}
async function* createAsyncGenerator() {
while (true) {
await sleep(500);
const value = yield;
console.log(value);
}
}
async function main() {
const asyncGen = createAsyncGenerator();
// No log at this step: the first value sent through `next` is lost
console.log(await asyncGen.next(1)); // { value: undefined, done: false }
// Logs 2: the value sent through `next`
console.log(await asyncGen.next(2)); // { value: undefined, done: false }
}
main();
規範
| 規範 |
|---|
| ECMAScript® 2026 語言規範 # sec-asyncgenerator-prototype-next |
瀏覽器相容性
載入中…