May 5, 2025 at 3:21:50 PM UTC

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TIL Chrome and Safari support dynamic creation of Import Maps in script 👀

Firefox does too but with a few *hefty* limitations:

1. “Import maps are not allowed after a module load or preload has started” (separate non-module `<script>`)
2. “Multiple import maps are not allowed.” 😭

let importMap = { imports: { "@zachleat/noop": "https://unpkg.com/@zachleat/noop@1.0.4/index.js" } }; let s = document.createElement("script"); s.type = "importmap"; s.innerHTML = JSON.stringify(importMap); document.body.appendChild(s);

Also posted to Mastodon.

15 replies

Alex Riviere Bluesky 4 min later

Ooooh
Julien W. Mastodon 18 min later

@zachleat Mmm there's a bug about the multiple import maps, but it doesn't look like it's actively worked on:
https://bugzilla.mozilla.org/show_bug.cgi?id=1916277
I'm not sure for your first comment, it might be worth filing a separate bug...
1. Zach Leatherman Mastodon 46 min later
  
  @julienw subscribed, thank you!
𝕮 Bluesky 21 min later

Any references your quoting? I was playing around with recently and I think Safari also requires importmaps to be dynamically created in a non-module script.
1. Zach Leatherman Bluesky 33 min later
  
  codepen.io/zachleat/pen... seems to work in Safari 18.4
  1. 𝕮 Bluesky 2 hr later
    
    Interesting! I just realized that I'm on a older version of Safari and this demo cant resolve the importmap!
    1. Zach Leatherman Bluesky 2 hr later
      
      a small and super casual cc to @alexis.deveria.com I know that caniuse has multiple import maps (via MDN) but I did not see dynamic import maps!
      1. Zach Leatherman Bluesky 2 hr later
        
        (though maybe I should file on github.com/mdn/browser-... ?)
        
        Fyrd Bluesky 4 hr later
        
        Yup, this seems like a good BCD entry as importmap sub-feature!
        
        Zach Leatherman Bluesky 4 hr later
        
        GitHub issues shepherded me to this repo, but I filed it thanks! github.com/mdn/mdn/issu...
Simon Pieters Bluesky 42 min later

bugzilla.mozilla.org/show_bug.cgi...
1. Zach Leatherman Bluesky 43 min later
  
  Subscribed, thank you!
Zach Leatherman Bluesky 1 hr later

(I was surprised to learn this was even possible!)
Yoav Weiss Bluesky 5 hr later

Blog post coming soon..
1. Zach Leatherman Bluesky 5 hr later
  
  ooh — looking forward to it!