Example steps for implementing class selectors and name attribute selectors in js

function getElementsByClass(className) {
   var classArr = [];
   var tags = document.getElementsByTagName("*");

   for (var i = 0; i < tags.length; i++) {
    if (tags[i].nodeType == 1) {
     if (tags[i].getAttribute("class") == className) {
      classArr.push(tags[i]);
     }
    }
   }
   return classArr;
}

function getElementsByName(name) {
   var nameArr = [];
   var num = 0;
   var tags = document.getElementsByTagName("*");

   for (var i = 0; i < tags.length; i++) {
    if (tags[i].nodeType == 1) {
     if (tags[i].getAttribute("name") == name) {
      nameArr.push(tags[i]);
     }
    }
   }

   return nameArr;
}

  /** 
   * Recursively get all child nodes * 
   Node represents the parent node type value for which you want to obtain all child nodes:
   1 Element represents an element 2 Attr represents an attribute 3 Text represents the text content in an element or attribute 4 CDATASection represents a CDATA section in a document (text that will not be parsed by the parser)
   5 EntityReference represents entity reference 6 Entity represents entity 7 ProcessingInstruction represents processing instruction 8 Comment represents comment 9 Document represents the entire document (the root node of the DOM tree)
   10 DocumentType provides an interface to entities defined for a document 11 DocumentFragment represents a lightweight Document object that can hold a portion of a document 12 Notation represents a symbol declared in a DTD */
  var allChildNodes = function (node, type) {
   // 1. Create an array of all nodes var allCN = [];

   // 2. Recursively get all nodes var getAllChildNodes = function (node, type, allCN) {
    // Get all child nodes of the current element
    var nodes = node.childNodes;
    // Get the child nodes of nodes for (var i = 0; i < nodes.length; i++) {
     var child = nodes[i];
     // Determine whether it is a node of the specified type if (child.nodeType == type) {
      allCN.push(child);
     }
     getAllChildNodes(child, type, allCN);
    }
   }
   getAllChildNodes(node, type, allCN);
   // 3. Return the array of all nodes return allCN;
  }

  // Call:
  // Get all nodes in body allChildNodes(document.querySelector('body'), 1);
  
  //Get all the plain text nodes in body allChildNodes(document.querySelector('body'), 3)