<script>
let value;
let derivedArr = []
$: if (value) {
derivedArr = [...derivedArr, value]
}
function random () {
value = Math.floor(1 + Math.random() * 10)
}
</script>
<button on:click={random}>Generate Random Value</button>
<p>value: {value}</p>
<p>derivedArr: {derivedArr}</p>