svelte/test/runtime/samples/select-change-handler/main.html

<select bind:value="selected" on:change="updateLastChangedTo(selected)">
    {{#each options as option}}
    <option value="{{option.id}}">{{option.id}}</option>
    {{/each}}
</select>

<script>
export default {
    methods: {
        updateLastChangedTo(result) {
            this.set({ lastChangedTo: result })
        }
    }
}
</script>