Quick example of how to overwrite docs without a full GET request to fetch the _rev.

gistfile1.js

/*
 * A real quick example that shows you how to overwrite the entire contents of 
 * a document without doing a full GET to fetch the document's current _rev.
 * This can be dangerous depending on your application because you don't know 
 * what was written before you and you might be overwriting something
 * important.
 *
 * What it does:
 * 1. For the purposes of this test, it issues a PUT to create a document we 
 * can play with. If it already exists then that's cool.
 *
 * 2. Issue a HEAD to the document, which gets the _rev in the E-Tag header. 
 * This is the value we need to include in our new document so that
 * CouchDB/Cloudant know we aren't overwriting someone else's work.
 *
 * 3. Update our document that we want to store.
 *
 * 4. Issue a PUT of the new data.
 */
var sag = require('sag').server(); //use localhost defaults
var docID = 'someDocID';

sag.setDatabase('quick-test');

//Create the document that we're going to play with.
sag.put({
  id: docID,
  data: { _id: docID, abc: 123 },
  callback: function(resp, succ) {
    //only error out if the error we got wasn't a conflict
    if(!succ && resp._HTTP.status != 409) {
      throw new Error('Was not able to create the doc!');
    }

    //Now that everything is set up, time to issue our HEAD request
    sag.head({
      url: docID,
      callback: function(resp, succ) {
        //The new document that we're going to overwrite the old one with.
        var newDoc = {
          _id: docID,
          foo: 'bar'
        };

        if(!succ) {
          throw new Error('Was not able to HEAD the doc!');
        }

        newDoc._rev = JSON.parse(resp.headers.etag);

        sag.put({
          id: docID,
          data: newDoc,
          callback: function(resp, succ) {
            if(!succ) {
              throw new Error('Was not able to PUT the doc!');
            }

            console.log('Done!', resp);
          }
        });
      }
    });
  }
});