如何使循环同步？

Question

如何使这个循环同步？提前致谢.

码

// (...)

object = {
  'item1': 'apple',
  'item2': 'orange'
};

// (...)

for(var key in object) {

  // do something async...
  request.on('response', function (response) {
    response.on('data', function (chunk) {

      console.log('The message was sent.');

    });
  });

}

console.log('The for cycle ended.');

产量

The for cycle ended.
The message was sent.

我想看看这种类型的输出......

The message was sent.
The for cycle ended.

Answer 1

更新的答案:

更新你的更新问题,调用sendMessage是同步的,所以你必须调用一个异步的函数(如下所述).sendMessage未列在NodeJS文档中.您必须从它获得的任何来源中找到它的同步版本,或使用其回调机制:

var obj, keys, key, index;

// Define the object
obj = {
  'item1': 'apple',
  'item2': 'orange'
};

// Find its keys (you can just type in the array if they don't
// need to be discovered dynamically)
keys = [];
for (key in obj) {
    keys.push(key);
}

// Start the loop
index = 0;
process();

// This function gets called on each loop
function process() {
    // Are we done?
    if (index >= keys.length) {
        // Yes
        console.log("The cycle ended");
    }
    else {
        // No, send the next message and then
        // use this function as the callback so
        // we send the next (or flag that we're done)
        sendMessage(obj[keys[index++]], process);
    }
}

原答案:循环是同步的.你必须做一些像setTimeout什么使它*一*同步.

但是,您对NodeJS进行的调用可能不同步.xyzSync如果要进行同步调用,则必须调用事物的版本.

继续猜测你的意思,如果你想让循环*a*同步:

var obj, key;

// Define the object
obj = {
  'item1': 'apple',
  'item2': 'orange'
};

for (key in obj) {
  schedule(key);
}

function schedule(k) {
    setTimeout(function() {
        // Do something with obj[k]
    }, 0);
}