Why would my setTimeout() return a random number on screen when the callback function executed

I am trying to learn Svelte by building a quiz app.

What I wanted to achieve is that when the user has answered a question from the quiz, it automatically jumps to the next one. I set a setTimeout() of 1 second so the user has a bit of time to see if he has answered correctly or not before being directed to the next question.

This works but I find that every time the toNextQuestion() funtion runs, it would print a random number value on screen, like being added to DOM.

I google and it seems that a setTimeout() funtion would return a number value as its ID. but can I bypass it here?

What should I do to achieve the goal while not having a random number added to DOM?

My code is like:

<script>    const toNextQuestion = () => {        currentQ uestionIndex += 1;        correct = undefined;        questionAnswered = false;     };</script>  {#await promise}<p>...waiting</p>  {:then data}<h1>Question {currentQuestion} of {data.results.length}</h1><em>Score: {score}</em>    {#each data.results as questionData, index}        {#if index === currentQuestionIndex}<Question                {questionData}                {questionAnswered}                {answerQuestion}                {evaluateAnswer}            />        {/if}    {/each}    {#if questionAnswered}        {setTimeout(() => {toNextQuestion()}, 1000)}<!-- Here it would add a random number TODO -->    {/if}    {#if currentQuestionIndex == data.results.length - 1}<!-- Here for completing the quiz TODO -->    {/if}{/await}

Any advice would be appreciated ! Thank you so much!