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Using String Interpolation Inside of Phoenix HEEx Template Tags


This came up recently while updating an application to use Phoenix 1.6 and wanting to add a variable to a list of HTML classes.

Quick Jump: Demo Video

My open source Docker / Phoenix example app was updated a few hours after the 1.6 release but I wasn’t sure how to do string interpolation with HEEx templates. Turns out it was pretty easy. You can do {"hey #{name}"} and you’re done! This wasn’t mentioned in the docs or 1.6 guide at the point of recording this video.

The example below is in the context of wanting to set a dynamic Tailwind class based on a flash message being an error, info, warning, etc..

Demo Video


  • 0:42 – The TL;DR version of using HEEx templates
  • 1:52 – How would you combine a few hard coded string classes and a variable?
  • 2:18 – Shout-out to Jose Valim for patching Live View within minutes
  • 3:14 – Showing how to do string interpolation in HEEx
  • 5:32 – Using your prior knowledge to help learn new things by breaking it down
  • 6:56 – Setting up a flash message to see how it looks

What do you think about HEEx templates overall? Let me know below.

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