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fix: hydration mismatch in Svelte 5 #162

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fix: hydration mismatch in Svelte 5 #162

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15 changes: 12 additions & 3 deletions packages/number-flow/src/lite.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -23,7 +23,7 @@ import type { Plugin } from './plugins'

export { define } from './util/dom'
export { prefersReducedMotion } from './styles'
export { renderInnerHTML } from './ssr'
export { renderInnerHTML, renderFallback } from './ssr'
export * from './plugins'
export * from './formatter'

Expand Down Expand Up @@ -124,6 +124,10 @@ export default class NumberFlowLite extends ServerSafeHTMLElement implements Pro
* @internal
*/
set data(data: Data | undefined) {
// Always remove DSD template from light DOM to prevent accumulation on re-renders
// (e.g., when framework wrappers re-render with {@html renderInnerHTML()})
this.querySelector('template[shadowrootmode]')?.remove()

if (data == null) {
return
}
Expand All @@ -134,8 +138,13 @@ export default class NumberFlowLite extends ServerSafeHTMLElement implements Pro
if (!this.created) {
this._data = data

// This will overwrite the DSD if any:
this.attachShadow({ mode: 'open' })
// Reuse existing shadow root from DSD if available, otherwise create one
if (!this.shadowRoot) {
this.attachShadow({ mode: 'open' })
} else {
// Clear DSD content to rebuild with JavaScript
this.shadowRoot.innerHTML = ''
}

try {
this._internals ??= this.attachInternals()
Expand Down
12 changes: 7 additions & 5 deletions packages/number-flow/src/ssr.ts
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Expand Up @@ -39,8 +39,13 @@ const renderPart = (part: KeyedNumberPart) =>
const renderSection = (section: KeyedNumberPart[], part: string) =>
`<span part="${part}">${section.reduce((str, p) => str + renderPart(p), '')}</span>`

export const renderFallback = (data: Data) =>
html`<span
style="font-kerning: none; display: inline-block; line-height: ${charHeight} !important; padding: ${maskHeight} 0;"
>${data.valueAsString}</span
>`

export const renderInnerHTML = (data: Data) =>
// shadowroot="open" non-standard attribute for old Chrome:
html`<template shadowroot="open" shadowrootmode="open"
><style>
${styles}</style
Expand All @@ -52,7 +57,4 @@ export const renderInnerHTML = (data: Data) =>
)}</span
>${renderSection(data.post, 'right')}</span
></template
><span
style="font-kerning: none; display: inline-block; line-height: ${charHeight} !important; padding: ${maskHeight} 0;"
>${data.valueAsString}</span
>` // ^ fallback for browsers that don't support DSD
>${renderFallback(data)}` // ^ fallback for browsers that don't support DSD
3 changes: 1 addition & 2 deletions packages/svelte/src/lib/NumberFlow.svelte
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Expand Up @@ -34,7 +34,6 @@
import type { HTMLAttributes } from 'svelte/elements'
import { writable } from 'svelte/store'
import { getGroupContext } from './group.js'
import { BROWSER } from 'esm-env'

export let locales: Intl.LocalesArgument = undefined
export let format: Format | undefined = undefined
Expand Down Expand Up @@ -102,5 +101,5 @@
__svelte_digits={digits}
{data}
>
{@html BROWSER ? undefined : renderInnerHTML(data)}
{@html renderInnerHTML(data)}
</number-flow-svelte>