如何queue.js工作？ [英] How does queue.js work?

问题描述

我一直在试图了解如何迈克·博斯托克的queue.js 工作，但我看不出它如何管理工作。我不明白的部分是如何code设法继续执行回调。特别是，我不能确定有关 POP（）方法（第45行）。从我的理解，该方法将在下次未处理，延迟功能;附加在队列中（潜在地）开始下一个延迟功能，当立即弹出功能完成执行的回调;那么最终执行表示的功能。我的问题是：什么code执行这个回调？

I've been trying to understand how Mike Bostock's queue.js works, but I can't see how it manages to work. The part I don't understand is how the code manages to continue executing callbacks. In particular, I am unsure about the pop() method (line 45). From my understanding, the method takes the next unprocessed, deferred function; appends a callback that (potentially) starts the next deferred function in the queue and executes when the immediately popped function finishes; then finally executes said function. My question is: what code executes this callback?

推荐答案

每个推迟功能实际上并不返回任何东西 - 他们预计执行其最后一个参数作为回调。例如，这是不行的。

Each deferred function does not actually return anything -- they are expected to execute their final argument as a callback. For example, this will not work

var foo = function(i) {
  console.log(i);
  return i;
}
var finished = function(error, results) {
  console.log(results);
}

queue(2)
  .defer(foo, 1)
  .defer(foo, 2)
  .defer(foo, 3)
  .defer(foo, 4)
  .awaitAll(finished);  // only prints "1" and "2", since foo() doesn't execute callbacks

不过，如果我们修改富来采取一个回调，

var foo = function(i, callback) {
  console.log(i);
  callback(null, i);  // first argument is error reason, second is result
}

然后，它会，作为执行回调的原因队列继续。

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