TypeError reading '_emitClasses' when instance is destroyed before first update (Vue and React)

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• I confirm

Reproduction link

https://e7webbe6.stackblitz.io (Vue), https://uqcs9xky.stackblitz.io (React)

Bug description

onUpdated in swiper-vue.mjs calls emitSlidesClasses() without checking destroyed. The updateSwiper branch a few lines below does check it.

onUpdated(() => {
  if (!initializedRef.value && swiperRef.value) {
    swiperRef.value.emitSlidesClasses();   // no destroyed check
    initializedRef.value = true;
  }
  ...
  if ((changedParams.length || breakpointChanged.value) && swiperRef.value && !swiperRef.value.destroyed) {

destroy(true) runs deleteProps(swiper), which removes swiper.params. emitSlidesClasses() then reads swiper.params._emitClasses and throws.

Two things have to line up. The instance must be destroyed before the component's first update, while initializedRef is still false. The Swiper must also have no slides, otherwise SwiperSlide's render throws first on swiperRef.value.params.loop.

The reproduction calls destroy(true, false), which is what the wrapper itself does in onBeforeUnmount. We hit it on a fast route change, where the component renders once and unmounts in the same Vue flush, so the queued onUpdated runs after the instance was destroyed. The throw happens inside Vue's post-flush queue, so the rest of that batch never runs and other components stop updating.

Fix:

-  if (!initializedRef.value && swiperRef.value) {
+  if (!initializedRef.value && swiperRef.value && !swiperRef.value.destroyed) {

swiper-react.mjs has the same unguarded call and throws the same way:

useEffect(() => {
  if (!initializedRef.current && swiperRef.current) {
    swiperRef.current.emitSlidesClasses();   // no destroyed check
    initializedRef.current = true;
  }
});

React reproduction: https://uqcs9xky.stackblitz.io (swiper 14.2.0, react 18.3.1)

There it takes even less to hit. That effect runs after layout effects, so destroying the instance from a layout effect is enough and no update is needed, it throws on mount. The sandbox has an error boundary so the message stays on screen. Without one the error reaches the root and React unmounts the whole tree, leaving a blank page.

Expected Behavior

onUpdated skips a destroyed instance, the same way the updateSwiper branch below it does. No error is thrown.

Actual Behavior

TypeError: Cannot read properties of undefined (reading '_emitClasses')
    at Swiper.emitSlidesClasses (swiper-core.mjs)
    at swiper-vue.mjs (onUpdated)

React:

TypeError: Cannot read properties of undefined (reading '_emitClasses')
    at _Swiper.emitSlidesClasses (swiper-core.mjs)
The above error occurred in the <Swiper> component

Swiper version

12.0.3 (also present in 14.2.0)

Platform/Target and Browser Versions

macOS 26.6.2, Chrome 152.0.7977.66; Vue 3.5.40 and React 18.3.1, Vite 6

Validations

• Follow our Code of Conduct
• Read the docs.
• Check that there isn't already an issue that request the same feature to avoid creating a duplicate.
• Make sure this is a Swiper issue and not a framework-specific issue

Would you like to open a PR for this bug?

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