Javascript Selection Engine without using querySelector or querySelectorAll

html_element_selector.js

var $ = function (selector) {
  var splitSelector = selector.split(/(?=\.)|(?=#)/);
 
  /* elemAttributes object provided for:
     1) DOM NodeName - only grabbing the first matched
     2) List of classes
     3) List of ID's - only grabbing the first matched
     
     pushes result in corresponding array in elemAttr object
     elName & classList use an array to capture all values provided
  */
  var elemAttributes = { elName: [], idName: [], classList: [] };
  splitSelector.forEach(function(subStr) {
    if (subStr.charAt(0) === '#') {
      elemAttributes.idName.push(subStr.substr(1));
    } else if (subStr.charAt(0) === '.') {
      elemAttributes.classList.push(subStr.substr(1));
    } else {
      elemAttributes.elName.push(subStr.toUpperCase());
    }
  });
 
  var filterById = function(nodes) {
    var matchedId = [];
    for (var i = 0; i < nodes.length; i++) {
      if (nodes[i].id === elemAttributes.idName[0]) {
        matchedId.push(nodes[i]);
        break;
      }
    }
    return matchedId;
  };
  
  var filterByClasses = function(nodes) {
    var matchedClasses = [];
    for (var i = 0; i < nodes.length; i++) {
      var nodeClassList = nodes[i].className.split(' ');
      for (var j = 0; j < nodeClassList.length; j ++) {
        // search for class in classList array
        if (elemAttributes.classList.indexOf(nodeClassList[j]) !== -1) {
          matchedClasses.push(nodes[i]);
          break;
        }
      }
    }
    return matchedClasses;
  };
 
  var filterByTagName = function(nodes) {
    var filtered = [];
    
    if (elemAttributes.idName.length > 0) {
      filtered = filtered.concat(filterById(nodes));
    } else if (elemAttributes.classList.length > 0) {
      filtered = filtered.concat(filterByClasses(nodes));
    } else {
      filtered = filtered.concat(nodes);
    }
 
    return filtered;
  };
 
 
  var getElements = function() {
    var nodes, elements = [];
    if (elemAttributes.elName.length > 0) {
      nodes = document.getElementsByTagName(elemAttributes.elName[0]);
      nodes = filterByTagName([].slice.call(nodes));
    } else if (elemAttributes.idName.length > 0) {
      nodes = document.getElementById(elemAttributes.idName[0]);
    } else if (elemAttributes.classList.length > 0) {
      var classList = elemAttributes.classList.join(' ');
      nodes = document.getElementsByClassName(classList);
      nodes = [].slice.call(nodes); // transforms HTMLCollection to array
    }
 
    elements = elements.concat(nodes);
    return elements;
  };
 
  return getElements();
};