我听说过JavaScript中的“yield”关键字，但我发现关于它的文档非常糟糕。有人能给我解释一下(或者推荐一个解释它的网站)它的用法和用途吗?
当前回答
异步javascript调用之间的依赖关系。
另一个关于如何使用yield的好例子。
函数请求(url) { Axios.get (url).then((response) => { it.next(响应); }) ｝ 函数* main() { Const result1 = yield request('http://some.api.com'); Const result2 = yield request('http://some.otherapi?Id =' + result1。id); console.log('您的响应是:' + result2.value); ｝ Var it = main(); it.next ()
其他回答
举个简单的例子:
const strArr = ["red", "green", "blue", "black"];
const strGen = function*() {
for(let str of strArr) {
yield str;
}
};
let gen = strGen();
for (let i = 0; i < 5; i++) {
console.log(gen.next())
}
//prints: {value: "red", done: false} -> 5 times with different colors, if you try it again as below:
console.log(gen.next());
//prints: {value: undefined, done: true}
使用yield关键字的斐波那契序列生成器。
function* fibonacci() {
var a = -1, b = 1, c;
while(1) {
c = a + b;
a = b;
b = c;
yield c;
}
}
var fibonacciGenerator = fibonacci();
fibonacciGenerator.next().value; // 0
fibonacciGenerator.next().value; // 1
fibonacciGenerator.next().value; // 1
fibonacciGenerator.next().value; // 2
在我看来，MDN文档非常好。
The function containing the yield keyword is a generator. When you call it, its formal parameters are bound to actual arguments, but its body isn't actually evaluated. Instead, a generator-iterator is returned. Each call to the generator-iterator's next() method performs another pass through the iterative algorithm. Each step's value is the value specified by the yield keyword. Think of yield as the generator-iterator version of return, indicating the boundary between each iteration of the algorithm. Each time you call next(), the generator code resumes from the statement following the yield.
异步javascript调用之间的依赖关系。
另一个关于如何使用yield的好例子。
函数请求(url) { Axios.get (url).then((response) => { it.next(响应); }) ｝ 函数* main() { Const result1 = yield request('http://some.api.com'); Const result2 = yield request('http://some.otherapi?Id =' + result1。id); console.log('您的响应是:' + result2.value); ｝ Var it = main(); it.next ()
给出一个完整的答案:yield的工作原理类似于return，但在发电机中。
对于通常给出的例子，其工作原理如下:
function *squareGen(x) {
var i;
for (i = 0; i < x; i++) {
yield i*i;
}
}
var gen = squareGen(3);
console.log(gen.next().value); // prints 0
console.log(gen.next().value); // prints 1
console.log(gen.next().value); // prints 4
但是yield关键字还有第二个用途。它可以用来向生成器发送值。
为了澄清，举个小例子:
function *sendStuff() {
y = yield (0);
yield y*y;
}
var gen = sendStuff();
console.log(gen.next().value); // prints 0
console.log(gen.next(2).value); // prints 4
它的工作原理是，将值2赋给y，在它停止在第一个yield(返回0)后将其发送给生成器。
这使我们能够看到一些非常时髦的东西。(查协程)
