javascript - setTimeout 和 setImmediate 之间的优先级

Question

我在 Node documentation 上读到了这个:

setImmediate(callback, [arg], [...])

To schedule the "immediate" execution of callback after I/O events callbacks and before setTimeout and setInterval

但是，我看到了相反的情况。setTimeout 在 setImmediate 之前执行。是否有人对此行为有解释，或有关 Node 事件循环的任何文档？

谢谢:)

代码:

var index = 0;

function test(name) {
    console.log((index++) + " " + name);
}

setImmediate(function() {
    test("setImmediate");
})

setTimeout(function() {
    test("setTimeout");
}, 0);

process.nextTick(function() {
    test("nextTick");
})

test("directCall");

输出:

0 directCall
1 nextTick
2 setTimeout
3 setImmediate

Answer 1

您应该检查一下 github issue

The event loop cycle is timers -> I/O -> immediates, rinse and repeat. The documentation is correct but incomplete: it doesn't mention that when you haven't entered the event loop yet (as is the case in your example), then timers come first - but only on the first tick. (In master. To complicate matters, things work slightly less deterministic in v0.10.)