在js promises中挣扎，foreach promises添加结果

Question

有人能帮我解决这个问题吗?我正在尝试检索使用webrtc发送的数据量。但我无法理解这些承诺。

我需要遍历发送者列表，但对于每个发送者，我需要等待承诺，然后才能继续下一个发送者。

// Reset datacounter
Client.DataUsed = 0;

// Get senders (audio/video)
const senders = Client.WebcamConnection.getSenders();

// Iterate through senders
senders.forEach(sender => {
    // Get the stats then await the promise using then
    sender.getStats().then(stat => {
        // Iterate through raports of stat
        stat.forEach(report => {
            // Check if is the right raport
            if (report.type === 'outbound-rtp') {
                // Add the byte count to the datacounter
                Client.DataUsed += report.bytesSent + report.headerBytesSent;
            }
        });
    });
});

// Do something with the Client.DataUsed

Answer 1

正如您所说，在所有承诺都确定之前，您不能使用结果。您可以使用Promise.all来等待它们，请参阅***注释：

// Reset datacounter
Client.DataUsed = 0;

// Get senders (audio/video)
const senders = Client.WebcamConnection.getSenders();

// ***Create an array of promises, one for each sender, and pass it into
// `Promise.all`***
Promise.all(senders.map(sender => {
    // *** Return the promise created by `then` so `Promise.all` can
    // wait for it***
    // Get the stats then await the promise using then
    return sender.getStats().then(stat => {
        // Iterate through raports of stat
        stat.forEach(report => {
            // Check if is the right raport
            if (report.type === 'outbound-rtp') {
                // Add the byte count to the datacounter
                Client.DataUsed += report.bytesSent + report.headerBytesSent;
            }
        });
    });
})
.then(() => {
    // Do something with the Client.DataUsed
})
.catch(error => {
    // Handle/report error
});