interface

uses
  ceflib;//其它

type
//这里建议用class  不建议用class(TThread)  不然有些地方要报错
TMyExtension = class(TThread) // or just class, (extension code execute in thread)
  public
  class function _geta:string;
end;

TCustomRenderProcessHandler = class(TCefRenderProcessHandlerOwn)
protected
    procedure OnWebKitInitialized; override;
end;

implementation

class function TMyExtension._geta: string;
begin
  Result:='调用成功';
end;

procedure TCustomRenderProcessHandler.OnWebKitInitialized;
begin
  TCefRTTIExtension.Register('JS_DELPHI', TMyExtension);
end;

initialization
  CefRenderProcessHandler := TCustomRenderProcessHandler.Create;

end.

<script> alert( JS_DELPHI._geta() ); <script>