ReactJS doubt

gistfile1.js

class Header extends React.Component{

  constructor(props, context) {
   super(props);
  }
  
  toggleAdvancedSearch() {

      React.render(
        <AdvancedSearch />, document.getElementById('advanced-widget'));
  }  

  search() {
        SearchActions.Search();        
  }

  render() {

    var Toolbar = mui.Toolbar;
    var ToolbarGroup = mui.ToolbarGroup;
    var DropDownMenu = mui.DropDownMenu;
    var DropDownIcon = mui.DropDownIcon;
    var RaisedButton = mui.RaisedButton;
    var TextField = mui.TextField;
    var IconButton = mui.IconButton;
    var FlatButton = mui.FlatButton;
    var FontIcon = mui.FontIcon;
    var DatePicker = mui.DatePicker;

    return(
           <header>
            <div className="mui-search-bar">
               <div id="search-block"> 
                <TextField hintText="02360" floatingLabelText="Enter Zip Code. Eg 02360" />
                <IconButton className="fa fa-search" id="search-btn" onClick={this.search}/>
               </div>            
                <span id="advanced-btn" onClick={this.toggleAdvancedSearch} >
                    Advanced <i className="fa fa-caret-down"></i>
                </span>
            </div>            
          </header>
        );
  }

}

class Header extends React.Component{

  constructor(props, context) {
    super(props);
    this.state({
      showAdvancedSearch: false
    })
  }

  toggleAdvancedSearch() {
    var searchContainer = document.querySelector("body #advanced-widget"); // can use any css selector: class / tag / etc.

    React.render(
      (!this.state.showAdvancedSearch ? <AdvancedSearch /> : null),
        searchContainer
    );

    this.setState({
      showAdvancedSearch: !this.state.showAdvancedSearch // Set the reverse state for showAdvancedSearch
    });
  }  

  handleSearch() {
    return SearchActions.Search();        
  }

  render() {
    var Toolbar = mui.Toolbar,
        ToolbarGroup = mui.ToolbarGroup,
        DropDownMenu = mui.DropDownMenu,
        DropDownIcon = mui.DropDownIcon,
        RaisedButton = mui.RaisedButton,
        TextField = mui.TextField,
        IconButton = mui.IconButton,
        FlatButton = mui.FlatButton,
        FontIcon = mui.FontIcon,
        DatePicker = mui.DatePicker;

    return(
      <header>
        <div className="mui-search-bar">
          <div id="search-block"> 
            <TextField hintText="02360" floatingLabelText="Enter Zip Code. Eg 02360" />
            <IconButton className="fa fa-search" id="search-btn" onClick={this.handleSearch}/>
          </div>       
          <span id="advanced-btn" onClick={this.toggleAdvancedSearch} >
            Advanced <i className="fa fa-caret-down"></i>
          </span>
        </div>            
      </header>
    );
  }

}