createElement.js

function createElement(tagName, config) {
    if (tagName instanceof Object) {
      config = tagName;
      tagName = null;
    }
    config = Object.assign({
      tagName: tagName || 'div',
      className: null,
      class: null,
      attr: null,
      events: {},
      target: null,
      content: null,
      children: []
    }, config || {});

    var element = document.createElement(config.tagName);

    if (config.className !== null) {
      element.className = config.className;
    }
    if (config.class instanceof Function) {
      var c = {};
      config.class = config.class(c) || c;
    }
    if (Array.isArray(config.class)) {
      element.className = config.class.join(' ');
    } else if (config.class instanceof Object) {
      for (var className in config.class) {
        if (!config.class.hasOwnProperty(className)) {
          continue;
        }
        if (!!config.class[className]) {
          element.classList.add(className);
        }
      }
    }

    if (config.attr instanceof Object) {
      for (var attr in config.attr) {
        if (config.attr.hasOwnProperty(attr)) {
          var value = config.attr[attr];
          if (value instanceof Function) {
            value = value();
          }
          if (typeof value !== "undefined") {
            element.setAttribute(attr, config.attr[attr]);
          }
        }
      }
    }


    for (var event in config.events) {
      if (config.events.hasOwnProperty(event)) {
        element.addEventListener(event, config.events[event]);
      }
    }

    if (config.content !== null) {
      element.innerHTML = config.content;
    } else if (config.children.length > 0) {
      config.children.forEach(function (child) {
        if (child instanceof Object) {
          child = createElement(child);
        } else if (typeof child === "string") {
          child = document.createTextNode(child);
        }
        if (child instanceof Node) {
          element.append(child);
        }
      });
    }

    if (config.target instanceof Node) {
      config.target.appendChild(element);
    }

    return element;
  }