function doesObjectExist() {
    cos.headObject({
        Bucket: 'examplebucket-1250000000', /* Enter your own bucket, required field */
        Region: 'COS_REGION',  /* The region where the bucket is located, such as ap-beijing, required field */
        Key: '1.jpg',  /* The object key stored in the bucket (e.g., 1.jpg, a/b/test.txt), required field */
    }, function(err, data) {
        if (data) {
            console.log('Object exists');
        } else if (err.statusCode == 404) {
            console.log('Object does not exist');
        } else if (err.statusCode == 403) {
            console.log('No read permission for this object');
}
    });
}

function(err, data) { ... }