Will build a mongodb fields list filter from a graphql query resolver

makeFieldList.js

///////////////////
// makeFieldList //
///////////////////

const filterString = '_r'
const reg = new RegExp(`${filterString}$`)

/**
 * @param  {Object[]}  fields      The selectionSet selections array from the resolver info arg.
 * @param  {Object}    [f={}]      Fields object, used with recursive calls
 * @param  {String}    [rootName]  Current obeject path, used with recursive calls
 * @return {Object}                Mongodb fields object
 */
const makeFieldList = (fields, f = {}, rootName) => {
  for (let i = 0; i < fields.length; i++) {
    const val = fields[i].name.value
    if (!reg.test(val)) {
      const newRoot = rootName ? `${rootName}.${val}` : val
      fields[i].selectionSet ? makeFieldList(fields[i].selectionSet.selections,
        f, newRoot) : f[newRoot] = 1
    }
  }
  return f
}