case user.length < 4; console.log("nametoo short :("); break; 为什么这不起作用？

Question

我正在处理 switch 语句，我一直在尝试使这里的代码正常工作，但它似乎没有输出正确的 console.log 大小写字符串。

var user = prompt("What is your name?").toLowerCase();
switch(user){
    case "luka":
    console.log("What a beautiful name, my name is exactly the same :) Hi Luka! :D");
    break;

    case user.length > 10:
    console.log("That's a long name!");
    break;

    case user.length < 4:
    console.log("Not to be rude or impolite to you in any way, but your name is kinda       short :( Not that it isn't cool or something :D");
    break;

}

我试过像这样 (user).length

Answer 1

你不应该在 switch 语句中使用条件。

使用 if/else if

var user = prompt("What is your name?").toLowerCase();
if (user==="luka") {
    console.log("What a beautiful name, my name is exactly the same :) Hi Luka! :D");
} else if (user.length > 10) {
    console.log("That's a long name!");
} else if (user.length < 4) {
    console.log("Not to be rude or impolite to you in any way, but your name is kinda       short :( Not that it isn't cool or something :D");
} else {
    console.log("in else");
}

Answer 2

在像您这样的情况下使用switch 有一种可能的解决方法：

var user = prompt("What is your name?").toLowerCase();
switch (true) {
    case (user === "luka"):
        console.log("What a beautiful name, my name is exactly the same :) Hi Luka! :D");
        break;

    case (user.length > 10):
        console.log("That's a long name!");
        break;

    case (user.length < 4):
        console.log("Not to be rude or impolite to you in any way, but your name is kinda       short :( Not that it isn't cool or something :D");
}

但是我会遵循 @epascarello's 的建议并使用 if/else 块。

Answer 3

这不是 JavaScript switch 语句的工作方式。 “case”表达式中的值与switch 表达式的值进行比较。

你那里的语句相当于：

if (user === "luka") {
    console.log("What a beautiful name, my name is exactly the same :) Hi Luka! :D");
}
else if (user === (user.length > 10)) {
    console.log("That's a long name!");
}
else if (user === (user.length < 4)) {
    console.log("Not to be rude or impolite to you in any way, but your name is kinda       short :( Not that it isn't cool or something :D");    
}

因此，您将“用户”的值与将user.length 与这些值进行比较的结果进行比较。这些比较结果是布尔值，因此“使用”对他们来说永远不会是===。