89 lines
4.8 KiB
JavaScript
89 lines
4.8 KiB
JavaScript
/**
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* embedScript — load another bundle's script and wait for its element to register.
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*
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* ★ WHAT AN APP SHELL DOES. A capability-5 plugin nests other plugins, so it needs three things:
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* work out the tree root it was served from, load a bundle's `.js` exactly once, and wait for the
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* custom element to actually exist before mounting it. Both shells in this repo — the Research
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* Gallery (`doxa-maps-spa`) and the Plugin Studio (`plugin-studio`) — had their own copy of all
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* three, identical in code (DEDUP-AUDIT.md, 2026-09-28: 33 lines, the only cross-plugin cluster
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* that is identical, closes over nothing, and spans one owner's plugins).
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*
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* Moved verbatim; the comments below are the originals, because each records a measurement.
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*
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* ★ ONE BEHAVIOUR CHANGE, AND IT IS AN IMPROVEMENT: `_loaded` is now shared. Two shells on one page
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* previously kept separate caches and would each load the same bundle. Now the second one reuses
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* the first's promise. Same result, one network request instead of two.
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*/
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/**
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* Load a bundle exactly once per URL; resolves after its script has executed.
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*
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* ★ A CLASSIC SCRIPT FIRES onload AND THEN FAILS, for a dev-server bundle. Measured 2026-09-22:
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* pointing a plain <script> at a dev entry (/plugin-designs/<bundle>/index.js, a real ES MODULE)
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* fires onload — so a loader watching onload reports SUCCESS — and only THEN throws "Cannot use
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* import statement outside a module" as an ASYNC page error. The tag is never defined,
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* document.createElement(tag) yields an inert HTMLUnknownElement, and the pane sits empty while its
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* own state reads 'ready'. onload is structurally incapable of seeing this, so it is not a usable
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* success signal by itself — which is why every mount below also waits on whenTagDefined().
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*
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* The built tree ships IIFEs, where a classic tag is correct, so this only ever bites under the dev
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* server — exactly the surface a developer works on. Rule: a rooted /plugin-designs/ entry (or any
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* .../index.js) is a dev ES module; everything else is a built IIFE.
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* MEASURED a second time, independently, on stack-demo's dev leaf 2026-09-22 (StackLayout, before it
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* used this file): 0 failed requests, and yet customElements.get('research-dashboard-map') === false
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* with 0 rows rendered. VerticalTabsLayout's private copy LACKED this rule until it moved here, so a
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* bundle nested through it on the dev server never defined its tag.
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*
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* An empty url is a no-op: a <script src=""> would re-fetch the page itself.
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*
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* SRI is optional (attrs.integrity).
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*/
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const _loaded = {}
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export function loadScriptOnce(url, attrs) {
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if (!url) return Promise.resolve()
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if (_loaded[url]) return _loaded[url]
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_loaded[url] = new Promise((ok, fail) => {
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const s = document.createElement('script')
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s.src = url
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if (/^\/plugin-designs\//.test(url) || /\/index\.js(\?|$)/.test(url)) s.type = 'module'
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if (attrs) for (const k in attrs) if (attrs[k]) s.setAttribute(k, attrs[k])
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s.onload = () => ok()
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s.onerror = () => { delete _loaded[url]; fail(new Error('failed to load ' + url)) }
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document.head.appendChild(s)
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})
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return _loaded[url]
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}
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// Wait for a tag to ACTUALLY register. loadScriptOnce resolving is not proof the element exists (see
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// above), and a module script's define() runs only after its import graph settles, so the tag can
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// appear a tick or two after onload. customElements.whenDefined is the browser's own authoritative
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// answer; the timeout turns a never-registered tag into THIS tab's error overlay rather than a silent
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// blank pane that claims to be ready.
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export function whenTagDefined(tag, ms) {
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if (typeof customElements === 'undefined') return Promise.resolve()
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if (customElements.get(tag)) return Promise.resolve()
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return Promise.race([
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customElements.whenDefined(tag),
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new Promise((_, fail) => setTimeout(() => {
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if (customElements.get(tag)) return
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fail(new Error('<' + tag + '> never registered (bundle loaded but defined no element)'))
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}, ms || 15000))
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])
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}
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/**
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* The tree root this shell was served from, with a trailing slash, or '' when it cannot be known.
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*
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* ⚠ READS document.currentScript, so it is only valid AT MODULE EVALUATION TIME. Call it once at the
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* top of an entry file (`const TREE_BASE = deriveTreeBase()`), never later — `currentScript` is null
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* once the script has finished executing, and a late call silently returns ''.
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*/
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export function deriveTreeBase() {
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try {
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const cur = (typeof document !== 'undefined' && document.currentScript && document.currentScript.src) || ''
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if (!cur) return ''
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// Strip the trailing "<bundle>/<bundle>.js" → the tree root, with trailing slash.
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const root = cur.replace(/[^/]+\/[^/]+$/, '')
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return root.replace(/\/+$/, '') + '/'
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} catch { return '' }
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}
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