The for await...of
语句在异步或者同步可迭代对象上(包括 String
,Array
,Array
-like 对象(比如arguments
或者NodeList
),TypedArray
,Map
, Set
和其他对象等等)创建一个迭代循环,调用自定义迭代钩子,并为每个不同属性的值执行语句。
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for await (variable of iterable) {
statement
}
variable
iterable
你还可以迭代一个明确实现异步迭代协议的对象:
var asyncIterable = {
[Symbol.asyncIterator]() {
return {
i: 0,
next() {
if (this.i < 3) {
return Promise.resolve({ value: this.i++, done: false });
}
return Promise.resolve({ done: true });
}
};
}
};
(async function() {
for await (num of asyncIterable) {
console.log(num);
}
})();
// 0
// 1
// 2
异步生成器已经实现了异步迭代器协议, 所以可以用 for await...of
循环。
async function* asyncGenerator() { var i = 0; while (i < 3) { yield i++; } } (async function() { for await (num of asyncGenerator()) { console.log(num); } })(); // 0 // 1 // 2
Specification | Status | Comment |
---|---|---|
ECMAScript Latest Draft (ECMA-262) ECMAScript Language: The for-in, for-of, and for-await-of Statements |
Draft |
Desktop | Mobile | Server | ||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
for await...of | Chrome Full support 63 | Edge No support No | Firefox Full support 57 | IE No support No | Opera Full support 50 | Safari Full support 11 | WebView Android Full support 63 | Chrome Android Full support 63 | Edge Mobile No support No | Firefox Android ? | Opera Android Full support 50 | Safari iOS ? | Samsung Internet Android ? | nodejs ? |