Save File using Greasemonkey

var data='col1,col2\nval1,val2';
var a = document.createElement('a');
a.href = 'data:application/csv;charset=utf-8,' + encodeURIComponent(data);
//supported by chrome 14+ and firefox 20+
a.download = 'data.csv';
//needed for firefox
document.getElementsByTagName('body')[0].appendChild(a);
//supported by chrome 20+ and firefox 5+
a.click();

DEMO

Maybe you can't write it to a local CSV, but you might be able to write it to say a Google Spreadsheet?

Yes you can do it using BLOB.

The script will attach content to a link that when clicked will offer to download a file (a file that never existed).

More info on:

• http://jsfiddle.net/UselessCode/qm5AG/
• How to create .txt file using JavaScript / HTML5?

---

This is how I did it (there are many other ways to do it):

1. GM (greasemonkey) script generates the content of the file
2. GM passes it to the web page using sessionStorage.variable="...content.."
3. script within page makes link visible and attach the content of the variable to the BLOB object.

You many need to stringify / parse the object.

• contacts=JSON.parse(sessionStorage.contacts)
• sessionStorage.contacts=JSON.stringify(contacts);

---

I modified slightly the original script to make it generic for multiple mime types.

Here is mine.

// Stuff to create the BLOB object   --- ANY TYPE ---
var textFile = null,
//-- Function
makeTextFile = function (text,textType) {
    // textType can be  'text/html'  'text/vcard' 'text/txt'  ...
    var data = new Blob([text], {type: textType });
    // If we are replacing a previously generated file we need to
    // manually revoke the object URL to avoid memory leaks.
    if (textFile !== null) {
      window.URL.revokeObjectURL(textFile);
    }
    textFile = window.URL.createObjectURL(data);
    return textFile;
  };

Hope it helps.

alternative approach could be if you fire a javascript controlled http request for each cvs line you have to a local http server applet that is capable of storing (simple cgi or apache/php could do it easy)