Open Bug 1425310 Opened 4 years ago Updated 3 months ago

Implement link rel="modulepreload"


(Core :: DOM: Core & HTML, enhancement, P3)

55 Branch




(Reporter: d, Unassigned)


(Blocks 1 open bug)


(Keywords: dev-doc-needed)

modulepreload is a new link relation that behaves similar to preload, but different in several key ways. For example, it interprets its attributes and changes to them differently; it uses the module map instead of the preload cache; and it allows optionally fetching descendant modules as an optimization.


Priority: -- → P3
Preloading is currently disabled and will be re-enabled by bug 1394778.
Depends on: 1394778
FWIW the processing module for modulepreload is unrelated to that for preload so I don't think bug 1394778 is actually a dependency.

Until recently (I'd need to parse Firefox versions to confirm when this occurred), web pages could leverage rel="preload" to ensure the early download of a JS file (and as spec'd early parsing) regardless of whether the script was later loaded as type="module" or not. However, the current experience is that while the preload occurs, a script included in the page as type="module" is then downloaded a second time. See as an example as discussed in

It seems Chrome is likely to move to this more strict interpretation of the rel="preload" spec and pages will need to move to rel="modulepreload" to get performance benefits in type="module" scripts anywhere, so I was hoping it would be possible to get an update on whether Firefox saw this as something they'd be able to implement.

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