Saving data from json to text file

Question

I have some temperature data in an html page returned from a raspberry using can bus. I want to save this data in a text file. The information exist in a JS file :

socket.on('tempback', (data) => {

  $("#BTInfo").text(data);

}); 

and i call it from the html so as to show it in an interface.

<div id="BPTInfo" class="number-circle text colortemp"> p id="BPTInf" style="vertical-align: middle;line-height: 1;margin-bottom: -1px;">0</p></div>

Please can you help me saving those data in a text file?