Can't set 'textContent' when Javascript-Vue/Nuxt 3 is null?

PhilippeUn
May 9, 2023
405 views
3 votes
3 Answers

I have a function that is supposed to change words every few seconds. Everything works as expected, but I get following error every few seconds in the VSC console:

TypeError: Cannot set properties of null (setting ‘textContent’) at
Timeout._onTimeout (…/components/home/Hero.vue:36:28) at
listOnTimeout (node:internal/timers:564:17)

I don’t understand why I get this error, because when I console.log word.value, I get the element. So I have access to it and the function is working, the words change every few seconds, as expected. I’m a bit confused and don’t know how to get the problem solved. I don’t get the error in the Google Chrome console, only in VSC.

<span ref="word"></span>

onMounted(() => {
  randomizeText()
  wordChanger
})

onBeforeRouteLeave(() => {
  clearTimeout(wordChanger)
})

const wordChanger = setInterval(randomizeText, 4000)

const word = ref(null)
const words = reactive(['Word-1', 'Word-2'])
let i = 0

function randomizeText() {
  i = randomNum(i, words.length)
  const newWord = words[i]

  setTimeout(() => {
    word.value.textContent = newWord
  }, 200) // time to allow opacity to hit 0 before changing word
}

function randomNum(num, max) {
  let j = Math.floor(Math.random() * max)

  // ensure diff num every time
  if (num === j) {
    return randomNum(i, max)
  } else {
    return j
  }
}

Answers

Instead of using the const word = ref(null) as refs. You can directly call it the constant word in your template. It should still work the same.

<template>
  <div>
    <span>{{ word }}</span>
  </div>
</template>

Inside the setTimeout function, change this word.value.textContent = newWord to this word.value = newWord.

Here is the updated codes. Tested and it works.

<script setup lang="ts">
onMounted(() => {
  randomizeText()
  wordChanger
})

onBeforeRouteLeave(() => {
  clearTimeout(wordChanger)
})

const wordChanger = setInterval(randomizeText, 4000)

const word = ref('') // UPDATED
const words = reactive(['Word-1', 'Word-2'])
let i = 0

function randomizeText() {
  i = randomNum(i, words.length)
  const newWord = words[i]

  setTimeout(() => {
    word.value = newWord // UPDATED
  }, 200) // time to allow opacity to hit 0 before changing word
}

function randomNum(num, max) {
  let j = Math.floor(Math.random() * max)

  // ensure diff num every time
  if (num === j) {
    return randomNum(i, max)
  } else {
    return j
  }
}
</script>
<template>
  <div>
    <span>{{ word }}</span>
  </div>
</template>

Hope that helps you.

This is probably a timing issue (element not mounted while it is being changed by the code)

You can do this without setting the textContent property dirctly, by using the v-html directive and just changing the referenced variable (ref)
Also, you can just start the interval in the onMounted() hook.

import {onMounted, reactive, ref} from "vue";
import {onBeforeRouteLeave} from "vue-router";

let wordChanger;

onMounted(() => {
    randomizeText()
    wordChanger = setInterval(randomizeText, 4000);
})

onBeforeRouteLeave(() => {
    clearTimeout(wordChanger)
})

let word = ref('Hoi')
const words = reactive(['Word-1', 'Word-2'])
let i = 0

function randomizeText() {
    i = randomNum(i, words.length)
    const newWord = words[i]

    setTimeout(() => {
        word.value = newWord
    }, 200) // time to allow opacity to hit 0 before changing word
}

function randomNum(num, max) {
    let j = Math.floor(Math.random() * max)

    // ensure diff num every time
    if (num === j) {
        return randomNum(i, max)
    } else {
        return j
    }
}

<span v-html="word"></span>

You probably are using the ref ‘word’ wrong and some other details I share below:-
note: I add comments to the lines I changed to help you understand better

setup() {
    

    const word = ref(null);
    const words = reactive(['Word-1', 'Word-2']);

    function randomizeText(i) {
      const p = randomNum(i, words.length);
      const newWord = words[p];

      setTimeout(() => {
        word.value = newWord;
      }, 200); // time to allow opacity to hit 0 before changing word
    }

    function randomNum(num, max) {
      let j = Math.floor(Math.random() * max);

      // ensure diff num every time
      if (num === j) {
        // notice here as well I use num instead of i
        return randomNum(num, max);
      } else {
        return j;
      }
    }
    
    const wordChanger = setInterval(randomizeText, 4000);
    
    onMounted(() => {
      randomizeText(0); // start with 0
      // wordChanger; // no need using this here
    });

    onBeforeRouteLeave(() => {
      clearTimeout(wordChanger);
    });

    return {
      word,
    };
  },

<span>{{ word }}</span>

here’s a demo:- https://stackblitz.com/edit/vue-rap7bb?file=src/components/HelloWorld.vue

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Can’t set ‘textContent’ when Javascript-Vue/Nuxt 3 is null?

Answers