<button class="btn-blue" id="button-1">Button 1</button>
<button class="btn-blue" id="button-2">Button 2</button>
<button class="btn-blue" id="button-3">Button 3</button>
 
<script>
var _ = (function () {

  // variables
  var methods = {};


  // methods
  methods.makeArray = function (nodelist) {
    return Array.from(nodelist);
  }
  methods.getFirst = function (selector) {
    return document.querySelector(selector);
  }
  methods.getAll = function (selector) {
    return methods.makeArray(document.querySelectorAll(selector));
  }
  methods.addClass = function (c, a) {
    a.forEach(element => element.classList.add(c));
  }
  methods.removeClass = function (c, a) {
    a.forEach(element => element.classList.remove(c));
  }


  // return public methods
  return methods;
})();

// _.toArray()
var arr = _.makeArray(document.querySelectorAll('button'));
console.log('_.makeArray()', arr);

// _.get()
var btn = _.getAll('#button-2');
console.log('_getAll()', btn);



</script>