function doesObjectExist() {
    cos.headObject({
        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) {
        if (data) {
            console.log('The object exists.');
        } else if (err.statusCode == 404) {
            console.log('The object does not exist.');
        } else if (err.statusCode == 403) {
            console.log ('no permission to read the object');
        }
    });
}

function(err, data) { ... }