我们可以用 ES6 Generator 做什么而不能用 for 循环? [英] What can we do with ES6 Generator that we cannot with for loop?

问题描述

我了解了 ES6 的特性，而 Generators 引起了我的注意.我想到的一件事是链接 Promise 对象，而我无法用循环来做.我们将能够做哪些其他机制，而我们以前无法做到?

I went trough ES6 features and Generators caught my eye. One thing that sprang to mind is chaining Promise objects, that I could not do with loops. What other mechanics we will be able to do, that we could not before?

我确实理解这是一个宽泛的问题，但目前除了 Promises 之外我想不出任何其他的东西.

I do understand this is broad question, still I can't think of anything but Promises at the moment.

推荐答案

通过使用 yield，可以在函数的控制流中的任何点暂停生成器，从而保存当前的执行状态(范围和堆栈).

By using yield, generators can be suspended at any point in the control flow of your function, saving your current state of execution (scope & stack).

如果没有生成器，这会更复杂:

Without generators, this is more complicated:

• 您需要明确跟踪状态
• 分支和(尤其是)循环控制结构需要以函数方式表示，即递归编写.

生成器通常用于遍历数据结构，创建一个简单的类似流的迭代器，按顺序生成所有元素.对于简单的例子，可以考虑树遍历或图中的 DFS/BFS.

Generators are generically useful for traversing data structures, creating a simple stream-like iterator that yields all elements in order. Think of tree traversal, or DFS/BFS in graphs for simple examples.

function* traverseTree(node) {
    if (node == null) return;
    yield* traverseTree(node.left);
    yield node.value;
    yield* traverseTree(node.right);
}

// vs (not sure):
function traverseTree(node) {
    var rl, l, r;
    return {
        next: function() {
            if (node == null && !r) return {done:true};
            if (!l) l = traverseTree(node.left);
            if (!(rl=l.next()).done)
                return rl;
            if (node != null) {
                var n = {value:node.value};
                node = null;
                r = traverseTree(node.right);
                return n;
            }
            return r.next();
        }
    }
}

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