code: function create (str) {
    createTmpElement.innerHTML = str
    if (!createTmpElement.children.length) {
      return null
    }
    let children = Array.prototype.slice.call(createTmpElement.children)
    createTmpElement.innerHTML = ''
    return children.length > 1 ? children : children[0]
  }
docs: Create a element by string
  
  @param {string} str Html string
  @return {HTMLElement}