cos.deleteObject({
    Bucket: 'examplebucket-1250000000', /* Your bucket name. Required. */
    Region: 'COS_REGION',  /* Bucket region, such as `ap-beijing`. Required. */
    Key: '1.jpg',  /* Object key stored in the bucket (such as `1.jpg` and `a/b/test.txt`). Required. */
}, function(err, data) {
    console.log(err || data);
});

function(err, data) { ... }

cos.deleteMultipleObject({
    Bucket: 'examplebucket-1250000000', /* Your bucket name. Required. */
    Region: 'COS_REGION',  /* Bucket region, such as `ap-beijing`. Required. */
    Objects: [
        { Key: '1.jpg' }, /* Object key stored in the bucket (such as `1.jpg` and `a/b/test.txt`). Required. */
        { Key: '2.txt' }, /* Object key stored in the bucket (such as `1.jpg` and `a/b/test.txt`). Required. */
    ]
}, function(err, data) {
    console.log(err || data);
});

var deleteFiles = function (marker) {
    cos.getBucket({
        Bucket: 'examplebucket-1250000000', /* Your bucket name. Required. */
        Region: 'COS_REGION',  /* Bucket region, such as `ap-beijing`. Required. */
        Prefix: 'a/',
        Marker:       marker,
        MaxKeys: 1000,
    }, function (listError, listResult) {
        if (listError) return console.log('list error:', listError);
        var nextMarker = listResult.NextMarker;
        var objects = listResult.Contents.map(function (item) {
            return {Key: item.Key}
        });
        cos.deleteMultipleObject({
            Bucket: bucket,
            Region: region,
            Objects: objects,
        }, function (delError, deleteResult) {
            if (delError) {
                console.log('delete error', delError);
                console.log('delete stop');
            } else {
                console.log('delete result', deleteResult);
                if (listResult.IsTruncated === 'true') deleteFiles(nextMarker);
                else console.log('delete complete');
            }
        });
    });
}
deleteFiles();

function(err, data) { ... }