处理结合案件与switch 语句中的重复案例

2022-01-19 00:00:00 optimization switch-statement case-statement javascript

是否可以合并共享作业的 case 并为不共享的作业重复 case，还是最好将每个作业分开?

Is it okay to combine cases that share assignments and repeat the case for assignments that are not shared, or is it preferred to just keep each separated?

用一个简单的例子来说明.. case 0 和 180 都包含 w = 330 所以他们被合并了；分配给 x 的值对于每个都不同，因此它们会重复执行 x 分配.

To illustrate with a simple example.. case 0 and 180 both include w = 330 so they have been combined; the value assigned to x is different for each so they are repeated to do the x assignment.

switch(window.orientation) {
    case   0:
    case 180:
        w = 330;
        //break
    case   0:
        x = '-180px';
        //break
    case -90:
    case  90:
        w = 480;
        x = '0';
        break;
    case 180:
        x = '-80px';
        break;
}

推荐答案

当 switch 语句中的每个元素执行多个操作时，最好不要重复相同的 case 两次.您可以通过总结同一 case 下的所有代码片段来轻松实现这一点.

When it comes to do more than one operation per element in a switch statement, it's always better to not repeat the same case twice. You can easily achieve this by summing up all the fragments of code that are under the same case.

例如，如果要对case 0执行操作A，对case 0执行操作B和 case 1 那么你应该这样做:

For example, if you want to perform operation A on case 0 and operation B on case 0 and case 1 then you should do something like this:

switch(variable) {
    case 0:
        // operation A;
    case 1:
        // operation B;
        break;
}

这将在 case 0 上同时执行操作 A 和 B，因为在 上没有 break>案例0.

This will execute both operation A and B on case 0, because there's no break on case 0.

现在假设你写了这样的东西:

Now let's assume you write something like this:

switch(variable) {
    case 1:
        x = 1;
        break;
    case 1:
        x = 2;
        break;
}

上面的代码最终会将值 1 赋给变量 x.第二个 case 1，说 x = 2 永远不会到达，因为第一个 case 1break 语句代码>.

The above code will end up assigning the value 1 to the variable x. The second case 1, saying x = 2 will never be reached, because of the break statement in the first case 1.

所以如果你必须对 case 0 和 case 1 执行不同的操作，但它们共享一些操作，那么最好将重复某些代码行的 case 分开而不是写两次 case 1，因为这样可以让你的代码更容易阅读，速度也更快.

So if you have got to perform different operations on case 0 and case 1, but they share some operation, that's better to separate the cases repeating some lines of code instead of writing case 1 twice, because this makes your code easier to read and slightly faster.

所以在你的代码中，实现你想要的最好的方法是这个:

So in your code, the best way to achieve what you want is this one:

switch(window.orientation) {
    case   0:
        x = '-180px';
        w = 330;
        break;
    case 180:
        x = '-80px';
        w = 330;
        break;
    case -90:
    case  90:
        w = 480;
        x = '0';
        break;
}

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