在Dom元素中所有的输入都是字符串，即使为输入框设置了type属性：type="number" 或者 type="range"。所以我们在处理输入值时就要记得转换类型。 但是在使用bind:value时就不需要担心了，贴心的Svelte已经帮我们处理好了。

In the DOM, every input value is a string. That’s unhelpful when you’re dealing with numeric inputs — type="number" and type="range" — as it means you have to remember to coerce input.value before using it. With bind:value, Svelte takes care of it for you:

<label>
	<input type="number" bind:value={a} min="0" max="10" />
	<input type="range" bind:value={a} min="0" max="10" />
</label>

<label>
	<input type="number" bind:value={b} min="0" max="10" />
	<input type="range" bind:value={b} min="0" max="10" />
</label>