alpinejs/alpine v1.9.4

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<div x-data="{ foo: 'bar' }" x-on:custom-event="foo = $event.detail.newValue">
    <span x-text="foo"></span>

    <button x-on:click="$dispatch('custom-event', {newValue: 'baz'})">Turn 'bar' to 'baz'</button>
</div>