Extending MarkLogic Sequences with array functions (based on https://gist.github.com/jmakeig/6898dfa2af428a230101f21b60fd047e and https://github.com/jmakeig/iterant)

1-sequence-prototype.js

Sequence.map = function*(iterable, fct, that) {
    if ('function' !== typeof fct) {
      throw new TypeError('fct must be a function');
    }
    for (const item of iterable) {
      yield fct.call(that || null, item);
    }
  };
  
  Sequence.prototype.map = function(fct, that) {
    return Sequence.from(Sequence.map(this, fct, that));
  }
  
  
  Sequence.reduce = function(iterable, fct, init) {
    let value = init, index = 0;
    for (const item of iterable) {
      value = fct.call(null, value, item, index++, this);
    }
    return value;
  };
  
  Sequence.prototype.reduce = function reduce(reducer, init) {
    return Sequence.reduce(this, reducer, init);
  };
  
  Sequence.prototype.filter = function filter(predicate, that) {
    return Sequence.from(Sequence.filter(this, predicate, that));
  
  };
  
  Sequence.filter = function*(iterable, predicate, that) {
    if ('function' !== typeof predicate) {
      throw new TypeError('predicate must be a function');
    }
    let index = 0;
    for (const item of iterable) {
      if (predicate.call(that || null, item, index++, iterable)) {
        yield item;
      }
    }
  };

2-add-data.js

declareUpdate();
xdmp.documentInsert("/store1.json", {"active":true,"count":7,"location":"Paris"}) 
xdmp.documentInsert("/store2.json", {"active":false,"count":9,"location":"Paris"}) 
xdmp.documentInsert("/store3.json", {"active":true,"count":12,"location":"Paris"}) 

3-search.js

  cts.search("Paris")
  .filter(doc => doc.root.active == true)
  .map(doc => doc.root.count)
  .reduce((accumulator, count) => accumulator + count, 0)