mapToQueryString

queryMap = {
  name: 'Timur',
  last_name: 'Meyster',
  email: '[email protected]'
  }

var turnMapToArray = function(queryMap) {
  var queryResult = []
  for (var key in queryMap) {
    queryResult.push([key, queryMap[key]])
  }
  return queryResult;
}

var joinArrayStrings = function(arrayStr) {

  return arrayStr.reduce(function(joinedArray, arrayItem) {
    return joinedArray.concat(arrayItem.join("="));
  }, [])
}

var convertToQueryStr = function(arrayKeyValueStr) {
  return arrayKeyValueStr.join("&");
}

console.log(convertToQueryStr(joinArrayStrings(turnMapToArray(queryMap))));