Only since creating this test case did I found out the preload story is suprisingle undetermined for modules, which is incredibly worrying given preloading of deep trees is absolutely necessary for performance. Reference - whatwg/fetch#486.
In this test case we load a deep module tree (999 modules), with a preload on the last module using:
<link rel="preload" as="script" href="lib/module999.js" />
Run a local server and open test.html.
- Safari: The preloaded resource appears to be used, but there is still an unused preload warning.
- Chrome 61.0.3154.0: The preloaded resource is not used, and there is an unused preload warning. Tracking at https://bugs.chromium.org/p/chromium/issues/detail?id=740886.
- Firefox 54.0.1: Stops loading after 100 modules despite there being more to load with no error or warning. Tracking at https://bugzilla.mozilla.org/show_bug.cgi?id=1379942 for the error, and https://bugzilla.mozilla.org/show_bug.cgi?id=1379945 for the preload bug.
- Edge: Pending testing.