Updating the status reason in large number of records

I need to change the status reason of large number of records(~50,000 records). I just discovered that it cannot be accomplished with REST API and will need to use SOAP API for this purpose. I need to achieve it with JavaScript in least time expensive function.

My algorithm is as follows.

Construct fetch query for FetchXML// looking for best time efficient library to retrieve the records efficiently.

While(morerecords)

               fetch(~5000 records)

Update StatusReason

My question will be to check the efficient javascript/Jquery functions to achieve this.

Thanks in advance!