...
The first gotcha is that you can't import an existing project, you will need to create a new one and copy your sources into the folder where you created your IntelliJ FlexJS project, here I chose a Web Application for this example but you can also choose a Web / Desktop / Mobile + Apllication Application / Library depending on what you are targeting.
...
Actually, I will use DataGridExample for the need needs of this demotutorial.
The first thing you will need to do will be to add the FlexJS SDK to IntelliJ.
...
2- Nagivate to and select the FlexJS SDK from <FLEXJS_INSTALL_FOLDER>. (I'm using the a nightly build here)
While this window is still open, click on Global Libraries, we will add the FlexJS SDK also as a library, that's the second gotcha.
1- Click on New Global Library, select <FLEXJS_INSTALL_FOLDER>\/frameworks\/libs. Then, remove frameworks\/libs\/player and frameworks\/libs\/air.
2- Rename the library to something meaningful, I choose to name mine "FlexJS Nightly Lib".
...
7- In Default options for modules, add: -load-config+=<FLEXJS_INSTALL_FOLDER>\/ide\/IDEA\/intellij-config.xml
8- Click OK to validate.
...