1 Commits (a9916053d9bbad77143d34dd7fdd5ed8b2394413)

Author	SHA1	Message	Date
Mathias Picker	a9916053d9	perf: use createElement instead of createElementNS for HTML elements (#18262) ... ## Summary The current wrapper always calls `document.createElementNS(namespace ?? NAMESPACE_HTML, tag, options)` — even for HTML elements (the >99% case), and even when `options` would be `undefined`. Two effects compound: 1. **Route HTML elements through `createElement`** — Blink has a fast path that skips the namespace lookup `createElementNS` always performs. 2. **Omit the trailing `undefined` argument** — V8/Blink take a slower path for `createElementNS(ns, tag, undefined)` (and `createElement(tag, undefined)`) than for the bare 2-arg form. This applies symmetrically to the SVG/MathML branch, where the wrapper now also avoids the `undefined` 3rd arg. The wrapper dispatches to the fastest call shape for every input — `{HTML, non-HTML}` × `{with is, without is}` × no `undefined` ever. ## Affects Every place Svelte constructs a DOM element internally: `<svelte:element>`, `run_scripts`, the per-component `<style>` injector, the `{@html}` wrapper, and the `<template>` element used to clone string templates. ## Numbers Measured in headless Chromium (Chromium 145) using the browser bench harness from #18261, 2–3 runs, median. Lower per-call is better; higher hz is better. ### Raw call shapes (what each shape costs in the browser) | | hz | per-call | | ------------------------------------------- | -------: | -------: | | `createElement(tag)` | ~1,210k | ~0.83 µs | | `createElement(tag, undefined)` | ~901k | ~1.11 µs | | `createElementNS(NS_HTML, tag)` | ~913k | ~1.10 µs | | `createElementNS(NS_HTML, tag, undefined)` | ~630k | ~1.59 µs | | `createElement(tag, { is })` | ~484k | ~2.07 µs | | `createElementNS(SVG_NS, tag)` | ~333k | ~3.01 µs | | `createElementNS(SVG_NS, tag, undefined)` | ~303k | ~3.30 µs | | `createElementNS(SVG_NS, tag, { is })` | ~245k | ~4.08 µs | Two stable effects fall out: - **Trailing `undefined` is consistently slower** than the bare form — ~26% on `createElement`, ~31% on `createElementNS` (HTML), ~10% on `createElementNS` (SVG). - **`createElement` skips a namespace lookup** that `createElementNS` always performs — ~32% delta for equal-shape calls (`createElement(tag)` vs `createElementNS(NS_HTML, tag)`). ### Per-case impact of this PR | Case (namespace, `is`) | Old wrapper call | Old hz | New wrapper call | New hz | Speedup | | ----------------------------- | --------------------------------------------- | --------: | ------------------------------ | --------: | ------: | | HTML, no `is` (dominant path) | `createElementNS(NS_HTML, tag, undefined)` | ~630k | `createElement(tag)` | ~1,210k | **~92%** (1.92×) | | HTML, with `is` | `createElementNS(NS_HTML, tag, { is })` | (slow) | `createElement(tag, { is })` | ~484k | similar to above (just the NS-skip) | | SVG/MathML, no `is` | `createElementNS(ns, tag, undefined)` | ~303k | `createElementNS(ns, tag)` | ~333k | **~10%** | | SVG/MathML, with `is` | `createElementNS(ns, tag, { is })` | ~245k | same | ~245k | no change | No measurable change in JSDOM (both shapes route through the same JS implementation there). The headline gain — **~92% on the dominant HTML-no-`is` path** — combines both effects roughly equally: dropping the `undefined` (~46%) and switching to `createElement` (~32%). Wrapper-vs-raw was also verified: the new wrapper measured to within ±2% of raw `document.createElement(tag)` for the HTML-no-`is` case, so the function-call indirection adds no measurable overhead. See #18261 for the benchmark and methodology. ## Test plan - [x] All 5881 runtime tests still pass (runtime-runes + runtime-legacy) - [x] `<svelte:element xmlns={null}>` correctly falls back to HTML (covered by existing `dynamic-element-dynamic-namespace` test) - [x] SVG/MathML namespaces still go through `createElementNS` - [x] Custom-element `is` option still honoured on both branches 🤖 Generated with [Claude Code](https://claude.com/claude-code) --------- Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>	4 months ago