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Dialog/Drawer: lock scroll on the root element to prevent layout shift #42545

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6d9d886
Dialog/Drawer: lock scroll on the root element to prevent layout shift
mdo Jun 23, 2026
135736d
Bump bundlewatch size thresholds
mdo Jun 25, 2026
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4 changes: 2 additions & 2 deletions .bundlewatch.config.json
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Original file line number Diff line number Diff line change
Expand Up @@ -34,15 +34,15 @@
},
{
"path": "./dist/js/bootstrap.bundle.js",
"maxSize": "82.5 kB"
"maxSize": "82.75 kB"
},
{
"path": "./dist/js/bootstrap.bundle.min.js",
"maxSize": "53.25 kB"
},
{
"path": "./dist/js/bootstrap.js",
"maxSize": "53.75 kB"
"maxSize": "54.0 kB"
},
{
"path": "./dist/js/bootstrap.min.js",
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12 changes: 8 additions & 4 deletions js/src/dialog-base.js
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Original file line number Diff line number Diff line change
Expand Up @@ -159,7 +159,11 @@ class DialogBase extends BaseComponent {
}

if (preventBodyScroll) {
document.body.classList.add(CLASS_NAME_OPEN)
// Lock scroll on the root element (not <body>) so it lands on the same
// element that carries `scrollbar-gutter: stable`. Co-locating them keeps
// the gutter reserved while the scrollbar is hidden, so the page doesn't
// shift (and the ::backdrop covers the gutter instead of leaving a strip).
document.documentElement.classList.add(CLASS_NAME_OPEN)
}
}

Expand All @@ -181,15 +185,15 @@ class DialogBase extends BaseComponent {
}
}

// Closes the native <dialog> and tears down body-scroll prevention.
// Closes the native <dialog> and tears down scroll prevention.
// Safe to call multiple times — close() is a no-op on a closed dialog.
_closeAndCleanup() {
this._element.close()
this._openedAsModal = false

// Only restore body scroll if no other modal dialogs are open
// Only restore scroll if no other modal dialogs are open
if (!document.querySelector('dialog[open]:modal')) {
document.body.classList.remove(CLASS_NAME_OPEN)
document.documentElement.classList.remove(CLASS_NAME_OPEN)
}
}

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18 changes: 9 additions & 9 deletions js/tests/unit/dialog.spec.js
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Original file line number Diff line number Diff line change
Expand Up @@ -15,7 +15,7 @@ describe('Dialog', () => {
afterEach(() => {
clearFixture()
clearBodyAndDocument()
document.body.classList.remove('dialog-open')
document.documentElement.classList.remove('dialog-open')

for (const dialog of document.querySelectorAll('dialog[open]')) {
dialog.close()
Expand Down Expand Up @@ -94,7 +94,7 @@ describe('Dialog', () => {

dialogEl.addEventListener('shown.bs.dialog', () => {
expect(dialogEl.open).toBeTrue()
expect(document.body.classList.contains('dialog-open')).toBeTrue()
expect(document.documentElement.classList.contains('dialog-open')).toBeTrue()
resolve()
})

Expand Down Expand Up @@ -251,7 +251,7 @@ describe('Dialog', () => {

dialogEl.addEventListener('hidden.bs.dialog', () => {
expect(dialogEl.open).toBeFalse()
expect(document.body.classList.contains('dialog-open')).toBeFalse()
expect(document.documentElement.classList.contains('dialog-open')).toBeFalse()
resolve()
})

Expand Down Expand Up @@ -460,8 +460,8 @@ describe('Dialog', () => {
dialogEl.addEventListener('shown.bs.dialog', () => {
expect(dialogEl.open).toBeTrue()
expect(dialogEl.classList.contains('dialog-nonmodal')).toBeTrue()
// Non-modal dialogs should not add dialog-open to body
expect(document.body.classList.contains('dialog-open')).toBeFalse()
// Non-modal dialogs should not add dialog-open to the root element
expect(document.documentElement.classList.contains('dialog-open')).toBeFalse()
resolve()
})

Expand Down Expand Up @@ -1036,7 +1036,7 @@ describe('Dialog', () => {
})

describe('stacked modals', () => {
it('should keep dialog-open on body when closing one of two open modal dialogs', () => {
it('should keep dialog-open on the root element when closing one of two open modal dialogs', () => {
return new Promise(resolve => {
fixtureEl.innerHTML = [
'<dialog id="dialog1" class="dialog"></dialog>',
Expand All @@ -1053,18 +1053,18 @@ describe('Dialog', () => {
})

dialog2El.addEventListener('shown.bs.dialog', () => {
expect(document.body.classList.contains('dialog-open')).toBeTrue()
expect(document.documentElement.classList.contains('dialog-open')).toBeTrue()
dialog1.hide()
})

dialog1El.addEventListener('hidden.bs.dialog', () => {
expect(dialog2El.open).toBeTrue()
expect(document.body.classList.contains('dialog-open')).toBeTrue()
expect(document.documentElement.classList.contains('dialog-open')).toBeTrue()
dialog2.hide()
})

dialog2El.addEventListener('hidden.bs.dialog', () => {
expect(document.body.classList.contains('dialog-open')).toBeFalse()
expect(document.documentElement.classList.contains('dialog-open')).toBeFalse()
resolve()
})

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12 changes: 6 additions & 6 deletions js/tests/unit/drawer.spec.js
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Original file line number Diff line number Diff line change
Expand Up @@ -16,7 +16,7 @@ describe('Drawer', () => {

afterEach(() => {
clearFixture()
document.body.classList.remove('dialog-open')
document.documentElement.classList.remove('dialog-open')
clearBodyAndDocument()

for (const dialog of document.querySelectorAll('dialog[open]')) {
Expand Down Expand Up @@ -255,15 +255,15 @@ describe('Drawer', () => {
})

describe('options', () => {
it('if scroll is enabled, should not add dialog-open class to body', () => {
it('if scroll is enabled, should not add dialog-open class to the root element', () => {
return new Promise(resolve => {
fixtureEl.innerHTML = '<dialog class="drawer"></dialog>'

const drawerEl = fixtureEl.querySelector('.drawer')
const drawer = new Drawer(drawerEl, { scroll: true, backdrop: false })

drawerEl.addEventListener('shown.bs.drawer', () => {
expect(document.body.classList.contains('dialog-open')).toBeFalse()
expect(document.documentElement.classList.contains('dialog-open')).toBeFalse()
drawer.hide()
})
drawerEl.addEventListener('hidden.bs.drawer', () => {
Expand All @@ -273,19 +273,19 @@ describe('Drawer', () => {
})
})

it('if scroll is disabled, should add dialog-open class to body', () => {
it('if scroll is disabled, should add dialog-open class to the root element', () => {
return new Promise(resolve => {
fixtureEl.innerHTML = '<dialog class="drawer"></dialog>'

const drawerEl = fixtureEl.querySelector('.drawer')
const drawer = new Drawer(drawerEl, { scroll: false })

drawerEl.addEventListener('shown.bs.drawer', () => {
expect(document.body.classList.contains('dialog-open')).toBeTrue()
expect(document.documentElement.classList.contains('dialog-open')).toBeTrue()
drawer.hide()
})
drawerEl.addEventListener('hidden.bs.drawer', () => {
expect(document.body.classList.contains('dialog-open')).toBeFalse()
expect(document.documentElement.classList.contains('dialog-open')).toBeFalse()
resolve()
})
drawer.show()
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7 changes: 5 additions & 2 deletions scss/_dialog.scss
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Original file line number Diff line number Diff line change
Expand Up @@ -59,8 +59,11 @@ $dialog-sizes: defaults(
// scss-docs-end dialog-sizes

@layer components {
// Prevent body scroll when dialog is open
.dialog-open {
// Prevent page scroll when a dialog is open. Applied to the root element so
// `overflow: hidden` sits on the same element as `scrollbar-gutter: stable`
// (see _root.scss): the gutter stays reserved while the scrollbar is hidden,
// so the page doesn't shift when a dialog opens.
:root.dialog-open {
overflow: hidden;
}

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2 changes: 1 addition & 1 deletion site/src/content/docs/guides/migration.mdx
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Original file line number Diff line number Diff line change
Expand Up @@ -177,7 +177,7 @@ Bootstrap 6 is a major release with many breaking changes to modernize our codeb
- Data key: `bs.modal` &rarr; `bs.dialog` (affects `Dialog.getInstance()` and `Dialog.getOrCreateInstance()`).
- CSS variables: `--modal-*` &rarr; `--dialog-*`.
- Backdrop: The `.modal-backdrop` DOM element and the legacy `util/backdrop` helper are gone — Dialog uses the native `::backdrop` pseudo-element with `backdrop-filter: blur()` support.
- Body scroll prevention: `.modal-open` on `<body>` &rarr; `.dialog-open` on the `<body>` element.
- Scroll prevention: `.modal-open` on `<body>` &rarr; `.dialog-open` on the root (`<html>`) element, so it pairs with `scrollbar-gutter: stable` and the page doesn't shift when a dialog opens.
- New variant classes: `.dialog-slide-up`, `.dialog-slide-down` (slide animations), `.dialog-instant` (no animation), `.dialog-static` (static backdrop bounce), `.dialog-nonmodal` (non-modal positioning), `.dialog-scrollable`.
- Non-modal support: Set `modal: false` or `data-bs-modal="false"` for non-modal dialogs.
- Dialog swapping: Triggers inside an open dialog can open a new dialog and close the current one automatically.
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