webpack构建的react（es6）在浏览器中有一个Uncaught TypeError

I have used the react.js in my project.I write react class by es6 syntax. And I build my react component with webpack, the bundle.js runs well but I found that I just can not run any other js after the bundle.js in my browser. When I run "var a = 0" in the console of browser, I got an error like this:I have used the react.js in my project.I write