在Javascript表达式中使用throw

Question

这是我想要做的:

var setting = process.env.SETTING || throw new Error("please set the SETTING environmental variable");
                                     ^^^^^

但是翻译抱怨"语法错误:意外的令牌抛出".

有没有办法在同一行中抛出异常,我们比较一个值是否为假？

Answer 1

throw是一个语句,而不是表达式,因此您不能将它用作另一个表达式的一部分.你必须分开它:

var setting = process.env.SETTING;
if (!setting) throw new Error("please set the SETTING environmental variable");

Answer 2

您可以利用javascript的功能特性:

var setting = process.env.SETTING || 
               function(){ 
                 throw "please set the SETTING environmental variable";
               }();
// es201x
var setting = process.env.SETTING || 
              (() => {throw `SETTING environmental variable not set`})();

或更通用创建一个函数来抛出错误并使用它:

function throwErr(mssg){
    throw new Error(mssg);
}

var setting = process.env.SETTING || 
               throwErr("please set the SETTING environmental variable");

Answer 3

有一个草案提案将 throw 表达式（类似于 C# 7 的throw 表达式）引入 JavaScript/ECMAScript：

TC39 提案：抛出表达式