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If you are only using a simple text editor and the command line to compile your code, the compile will detect the mistake before you can run the code.
Going Further
When looking through the myriad articles on ReactJS, it becomes clear that its fresh approach to UI composition allows developers to use many other frameworks to build their application. Just do a search for "ReactJS dialog" or "ReactJS pop-up views" and many solutions present themselves. But most, if not all, are awkward or cumbersome to produce.
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States can easily enhance your application's experience and are convenient to use. For a complex example, including transitions that use effects, look at the FlexJS Store demo that is packaged under "examples" with the FlexJS SDK.
Summary
While ReactJS is a new, powerful, and clever way to make browser-based applications, you are still left with developing and debugging JavaScript. While JSX adds more checking to your ReactJS source code, having a true compiler, with syntax and type checking, can save you a lot of time during development as well as improving the quality of the delivered code.
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