小主可能经常需要跟踪某个状态的变化情况，特别是在排查Bug的时候。

It’s often useful to be able to track the value of a piece of state as it changes over time.

小主是不是想到了使用console.log, 就像在addNumber中那样！？但是当打开浏览器控制台（可以点击地址栏右边的按钮打开），你会看到一条消息说“这条消息是不可克隆的”。

Inside the addNumber function, we’ve added a console.log statement. But if you click the button and open the console drawer (using the button to the right of the URL bar), you’ll see a warning, and a message saying the message could not be cloned.

别急小主，这是因为numbers是个响应代理, 我们有几种方法可以修复这个问题，比如使用$state.snapshot(...)创建一个非响应的 快照 ：

That’s because numbers is a reactive proxy. There are a couple of things we can do. Firstly, we can create a non-reactive snapshot of the state with $state.snapshot(...):

function addNumber() {
	numbers.push(numbers.length + 1);
	console.log($state.snapshot(numbers));
}

另外我们还可以使用$inspect符文（rune）自动地在状态改变时记录下它的快照。更贴心地是这些代码会在正式发布应用时（为正式生产构建时）自动剔除：

Alternatively, we can use the $inspect rune to automatically log a snapshot of the state whenever it changes. This code will automatically be stripped out of your production build:

function addNumber() {
	numbers.push(numbers.length + 1);
	console.log($state.snapshot(numbers));
}

$inspect(numbers);

另外还可以使用$inspect(...).with(fn)自定义信息展示方式。比如可以使用console.trace查看状态是在什么地方被改变的。

You can customise how the information is displayed by using $inspect(...).with(fn) — for example, you can use console.trace to see where the state change originated from:

$inspect(numbers).with(console.trace);

小主，你说Svelte是不是很贴心?!