javascript - 使用 Promise - 结果不返回

Question

我有以下内容:

    resolutionTestBuilder.buildTests().then(function(tests) {
        var s = tests; // checking result
    });

buildTests 看起来像这样:

resolutionTestBuilder.buildTests = function () {
    Promise.all([createAllResolutions(), deviceScanner.scanDevices()])
        .spread(function (resolutions, videoDevices) {
            var tests = [];
            resolutions.forEach(function (targetResolution) {
                videoDevices.forEach(function (videoDevice) {
                    tests.push({ device: videoDevice, resolution: targetResolution });
                });
            });
            return tests;
        });
}

createAllResolutions 如下所示:

 var createAllResolutions = function () {
    for (let y = maxHeight; y >= minHeight; y--) {
       resolutions.push(
          {x:x,y:y}
       );
    }
    return resolutions;
}

最后，scanDevices 如下所示:

deviceScanner.scanDevices = function() {
    navigator.mediaDevices.enumerateDevices().then(function(availableDevices) {
        var videoDevices = [];
        for (var i = 0; i < availableDevices.length; ++i) {
            if (availableDevices[i].kind === 'videoinput') {
                videoDevices.push({ label: availableDevices[i].label || 'camera ' + (videoDevices.length + 1), id: availableDevices[i].deviceId });
            }
        }
        return videoDevices;
    });
}

我看到的行为是 .spread 参数部分完整 - 我获得了 分辨率，但没有获得 videoDevices。这是我第一次尝试 promise (和 Bluebird )，所以我可能在这里遗漏了一些非常基本的东西 - 我做错了什么？

Answer 1

return来自then回调还不够，你需要return then()的 promise 调用从函数创建!

resolutionTestBuilder.buildTests = function () {
    return Promise.all([createAllResolutions(), deviceScanner.scanDevices()])
//  ^^^^^^
        .spread(function (resolutions, videoDevices) {
            …
        });
};
deviceScanner.scanDevices = function() {
    return navigator.mediaDevices.enumerateDevices().then(function(availableDevices) {
//  ^^^^^^
        …
    });
};