For my SO question http://stackoverflow.com/q/33175305/4825465

1. synchronous way.js

// collectionA and collectionB are arrays of Doc objects
collectionA = [];
collectionB = [];

addToCollectionB: function (newField1, newField2){
  var newDocB = new Doc(newField, newField2);

  // 1. If collection A is empty, push newDocB onto collection B, and stop
  if (collectionA.length == 0){
    collectionB.push(newDocB);
    return; // ends addToCollectionB()
  }

  // 2. Get the current collection A's first element
  var docA = collectionA[0];

  // 3. check loop condition
  while (docA.field2 > 0){

    // 4. check which of the two ways to modify newDocB
    if ( docA.field1 > 0 ){
      // 5. one way removes docA from collectionA
      newDocB.field1 -= docA.field1;
      collectionA.splice(0,1);
    } else {
      // 6. the other way breaks out of the loop
      newDocB.field1 = 0;
      break; // break out of the while loop
    }

    // 7. if collectionA is empty, break out of the loop
    if (collectionA.length == 0){
      break;
    }

    // 8. loads the new docA and continues to the next loop
    docA = collectionA[0];
  }

  // 9. Loop is done, check if newDocB needs to be saved
  if (newDocB.field1 >= 0) {
    collectionB.push(newDocB);
    return; // ends addToCollectionB()
  }
}