Javascript: Uncaught Error :downloads.onDeterminingFilename 的监听器太多

Question

代码如下:

assets.forEach(function(v) {

    var canvas = document.createElement('canvas');
    canvas.id     = "canvas";
    canvas.width  = 200;
    canvas.height = 150;
    var ctx = canvas.getContext("2d");

    var img = new Image();
    img.src = 'file:///path/to/file/' + v.name;
    img.onload = function () {
        ctx.drawImage(img, 0, 0, img.width, img.height-256, 0, 0, 200, 150);
    };
    document.getElementById('download').addEventListener('click',
        function() {
            chrome.downloads.download({
                url: canvas.toDataURL()
            });

            chrome.downloads.onDeterminingFilename.addListener(
                function(downloadItem, cb) {
                    console.log(downloadItem);
                    cb({
                        filename: 'path/to/file/thumb-' + v.name.split('_')[0] + '.png',
                        conflictAction: 'overwrite'
                    });
                    return true;
                }
            );
        },
    false
    );
});

如果文件夹中只有 1 个文件，则此方法有效。如果更多，则它将仅适用于单个文件。如何弄清楚它才能适用于许多文件？

请注意，它将新缩略图保存到初始图像所在的同一文件夹中。

Answer 1

你不能有多个 onDeterminingFilename 监听器:

onDeterminingFilename

During the filename determination process, extensions will be given the opportunity to override the target DownloadItem.filename. Each extension may not register more than one listener for this event.

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