Nuxt.js and $ref, why doesn't it see my ref?

Question

Vue.js

mounted() {
  let timer;
  window.addEventListener('scroll', () => {
    if(timer) clearTimeout(timer);
    timer = setTimeout(() => {
      let testHeight = this.$refs.testElem.offsetHeight;
    });
  });
}

Added to mounted()
When moving from another page to a page with this code. gives an error
Uncaught TypeError: Cannot read property 'offsetHeight' of undefined
But continues to work correctly.
How to fix this error?

Answer 1

Once it works, just check this.$ref.testElem for existence. And do not forget to delete handlers in beforeDestroy, otherwise the browser will send you events to the destroyed components :)

Answer 2

show the code from the elements in the template
or looking ahead, do this
this.$refs.testElem.$el.offsetHeight