I’m trying to learn how to use an mjs file in Dash. So far I have a file, example.mjs, in the assets folder. It contains this code // Export a named function export function greet(name) { return `Hello, ${name}!`; } // Export a default variable const PI = 3.14159; export default PI; when I ru…

Hi @Arick Actually, .mjs files do work in Dash. The error you had was because you can’t use import in a regular .js file. It also has to be a .mjs file. It’s ok to define functions in different files. Dash loads all the .js (and .mjs) file at the start. They are loaded by file name, sorted …

I’m having this exact same issue. I have several clientside callbacks in separate .js files that I would like to simplify by defining some reusable functions in a separate file. Here’s my simplified file structure: --> assets ----> clientside_callbacks ------> otd_callback.js ------> backlog_callb…

This idea might sound stupid (and I thought for a while if posting it) but did you try renaming the file to figure_functions.js? @Arick feedback would be appreciated

Not a stupid idea! I originally tried using figure_functions.js but that resulted in an error about imports not allowed outside of a module. I read in the docs that you could import modules using the .mjs file type. I was able to find a work around though - as you suggested, I changed the file to f…

I’m just guessing, but the error you got sounds like if at some point the browser tries to use the function defined in the mjs file and the corresponding file is then uploaded to the internal server. This server checks the mime type and does not recognize it as valid js and defaults to mime type tex…

I’d like some follow-up advice to this topic. I set up everything correctly and the browser was still complaining that the modules were returned as text/plain. After sparring with the AI, it told me: Dash allowing .mjs does not guarantee your local Python MIME registry knows .mjs. So it told me …

Hello @Tobs , Just because something has a certain ending doesnt automatically mean that is the mimetype that will be sent in the response from the server to the client. .mjs isnt a standard for Dash, so it doesnt know to set it as such. The client has to know what to expect in the response in order…

That doesn’t necessarily sound unlogical, but it is still strange behavior. I haven’t seen it mentioned anywhere that the mimetype for .mjs files has to be specifcally added in the Dash app. It is not mentioned in the Dash docs, nor is it mentioned in posts like these. So, this gives me the feeling …

No, I do not use .mjs, but I have ran into the mime-type issue before. It’s not really an issue of your computer knowing what is or isnt a certain extension, its about the browser. Here is a search in the repo for mimetype declared in the base dash: [image]

I will raise a GitHub issue with this question. If it is something that has to be configured manually by the developer, then it would be helpful if it is mentioned in the documentation pages. The error message in the browser is really unhelpful in understanding the real problem, so it’s very unintui…

Trouble Loading *.mjs file

Dash Python

Arick November 21, 2025, 4:42pm 7

Hello @AnnMarieW , thank you so much for your reply - this worked perfectly!

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Trouble Loading *.mjs file

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