How does the COS JavaScript SDK obtain the progress of file uploads?

The COS (Cloud Object Storage) JavaScript SDK obtains the progress of file uploads by using a callback function that tracks the upload status. This is typically achieved through the onProgress event handler, which is provided during the upload process.

When you initiate an upload, you can specify an onProgress function that will be called periodically as the upload progresses. This function receives an event object containing information about the current state of the upload, such as the number of bytes uploaded and the total number of bytes to be uploaded. This allows you to calculate the percentage of the upload that has been completed and update your application's UI accordingly.

Here's an example of how you might use the onProgress callback with the COS JavaScript SDK:

const cos = new COS({
    SecretId: 'YOUR_SECRET_ID',
    SecretKey: 'YOUR_SECRET_KEY'
});

const uploadFile = () => {
    const file = document.getElementById('file-input').files[0];
    const Bucket = 'examplebucket-1250000000'; // Replace with your bucket name
    const Region = 'COS_REGION'; // Replace with your region
    const Key = `object_name_${file.name}`;

    cos.putObject({
        Bucket,
        Region,
        Key,
        Body: file,
        onProgress: function(progressData) {
            console.log(JSON.stringify(progressData));
            // You can update your UI here based on progressData
        }
    }, function(err, data) {
        if (err) {
            console.error('Upload failed:', err);
        } else {
            console.log('Upload success:', data);
        }
    });
};

In this example, as the file is being uploaded to the COS, the onProgress function will log the progress data to the console. You can use this information to display a progress bar or other visual indicator of the upload's progress in your web application.

For more advanced features and better scalability, consider using Tencent Cloud's COS service, which offers robust APIs and SDKs for managing object storage efficiently.