JavaScript has a relatively unknown functionality which allows you to label statements.

JavaScript具有一个相对未知的功能，该功能允许您标记语句。

I’ve recently saw this feature used in Svelte to power reactive declarations, which are re-computed whenever the variables declared into the statement change:

我最近看到Svelte中使用了此功能来增强React式声明，只要声明中声明的变量发生更改，就会重新计算该声明：

$: console.log(variable)

They also allow to use a statement block, another feature of JavaScript that lets you define a block whenever you can define a statement:

它们还允许使用语句块 ，这是JavaScript的另一功能，可让您在定义语句时定义块：

$: {  console.log(variable)  console.log('another thing')  //...}

This may look strange, but it’s correct JavaScript. This statement block is assigned to the $ label.

这可能看起来很奇怪，但是它是正确JavaScript。 该语句块分配给$ 标签 。

The Svelte compiler internally will use this to power reactive declarations.

Svelte编译器内部将使用它来增强React式声明。

I never used this feature anywhere else, yet, but the primary use case is breaking out of a statement that is not the nearest enclosing loop or switch.

我从未在其他任何地方使用过此功能，但是主要用例是突破了不是最近的封闭循环或开关的语句。

Here’s a simple example to explain what I mean.

这是一个简单的例子来解释我的意思。

Calling break in any of those points breaks out of the switch, to avoid running the other cases:

在这些点中的任何一个上调用break都会脱离该开关，以避免运行其他情况：

for (let y = 0; y < 3; y++) {  switch (y) {    case 0:      console.log(0)      break    case 1:      console.log(1)      break    case 2:      console.log(2)      break  }}

This will print 0 1 2 to the console, as expected.

按预期，这会将0 1 2打印到控制台。

But what if we want to break out of for when we reach case 1? Here is how:

但是，如果我们想在case 1突围而出， for怎么办？ 方法如下：

loop: for (let y = 0; y < 3; y++) {  switch (y) {    case 0:      console.log(0)      break    case 1:      console.log(1)      break loop    case 2:      console.log(2)      break  }}

This will print 0 1 to the console.

这会将0 1打印到控制台。

翻译自: