什么是JavaScript中的“function *”？

What is “function*” in JavaScript?

在这个页面中，我发现了一个新的javascript函数类型：

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// NOTE:"function*" is not supported yet in Firefox.
// Remove the asterisk in order for this code to work in Firefox 13

function* fibonacci() { // !!! this is the interesting line !!!
let [prev, curr] = [0, 1];
for (;;) {
[prev, curr] = [curr, prev + curr];
yield curr;
}
}

我已经知道yield、let和[?,?]=[?,?]是做什么的，但不知道function*是什么意思。这是怎么一回事？

另外，不要费心去尝试谷歌，搜索带有星号的表达式是不可能的(它们被用作占位符)。

相关讨论

这是一个发生器功能。

Generators are functions which can be exited and later re-entered. Their context (variable bindings) will be saved across re-entrances.

Calling a generator function does not execute its body immediately; an iterator object for the function is returned instead. When the iterator's next() method is called, the generator function's body is executed until the first yield expression, which specifies the value to be returned from the iterator or, with yield*, delegates to another generator function.

历史记录：

这是为EcmaScript.next建议的语法。

Mozilla的Dave Herman做了一个关于ecmascript的演讲。30:15他谈到发电机。

早些时候，他解释了Mozilla是如何实验性地实现所提议的语言变化来帮助指导委员会的。Dave与BrendanEich、Mozilla的CTO(我认为)和最初的JavaScript设计师密切合作。

您可以在ecmascript工作组wiki上找到更多详细信息：http://wiki.ecmascript.org/doku.php？id=和谐：发电机

工作组(TC-39)同意ecmascript.next应该有某种生成器迭代器建议，但这不是最终的建议。

在下一个版本的语言没有改变的情况下，您不应该依赖于这种显示，即使它没有改变，它可能在一段时间内不会在其他浏览器中广泛显示。

Overview

First-class coroutines, represented as objects encapsulating suspended execution contexts (i.e., function activations). Prior art: Python, Icon, Lua, Scheme, Smalltalk.

Examples

The"infinite" sequence of Fibonacci numbers (notwithstanding behavior around 253):

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function* fibonacci() {
let [prev, curr] = [0, 1];
for (;;) {
[prev, curr] = [curr, prev + curr];
yield curr;
}
}

Generators can be iterated over in loops:

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for (n of fibonacci()) {
// truncate the sequence at 1000
if (n > 1000)
break;
print(n);
}

Generators are iterators:

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let seq = fibonacci();
print(seq.next()); // 1
print(seq.next()); // 2
print(seq.next()); // 3
print(seq.next()); // 5
print(seq.next()); // 8