在javascript中嵌套'切换'案例：任何速度优势？ [英] nesting 'switch' cases in javascript: any speed advantage?

问题描述

新手问题：我有一个包含大量字符串的开关。按字母顺序分割它有速度优势吗？

newbie question here: I have a 'switch' containing numerous strings. Is there a speed advantage in splitting it alphabetically, like this?

switch(myString.substring(0,1)){
case "a" : switch(myString){
           case "a string beginning with a"       : runCode(); break;
           case "another string beginning with a" : runCode(); break;
           } break;
case "b" : switch(myString){
           case "by golly another string"         : runCode(); break;
           case "blimey - hundreds of strings"    : runCode(); break;
           //... etc

或者，无论如何，脚本语言都会读取每一行，只是找到封闭的括号？

Or does a scripted language read every line anyway, just to find the closed brackets?

推荐答案

是和否。您会看到最低速度增益，但不值得从这种结构中丢失代码可读性。 switch语句就像if-else语句的巨大块。它必须从一个案例转到另一个案例，直到它找到它正在寻找的东西，就像if-elseif-else结构相当于它。因此，你所做的只是帮助它跳过一些条件。嵌套的switch语句，特别是这里编写的方式，对于大多数开发人员而言，其可读性低于直接if-elseif-else层次结构。

Yes and no. You'd see a minimum speed gain, but not worth the code readability lost from this sort of structure. A switch statement is like a giant block of if-else statements. It has to go from one case to another until it finds what it's looking for, just like with the if-elseif-else structure equivalent to it. Thus all you're doing is to helping it skip over a handful of conditions. The nested switch statements, especially the way written here, are less readable for most developers than a straight up if-elseif-else hierarchy.

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