Why value property on input element on svelte is not working?

I want to manage the value of a state (to make custom validations, so I won't use bind:value) to pass into my input, but the value displayed in the input is not the value I have in the a state, why happend that?

<script lang="ts">  let a = "";  const onChange = (e: any) => {    const nv = e.target.value;    if (nv.length <= 4) {      a = nv;    }  };</script><div>value:{a}</div><input type="text" value={a} on:input={onChange} />