Question

我来自Ruby世界，后来进入JavaScript世界。 Ruby语言的一项功能是case语句，用于评估目标值：

my_val = case my_var
           when "var1" then "value1"
           when "var2" then "value2"
           else "value3"
         end

# my_val evaluated to a specific value 
puts my_val

我可以像上面的JavaScript一样简洁吗？这是我得到的最接近的东西：

let myVal = null;
switch (myVar) {
  case "var1": 
    myVal = "value1";
    break;
  case "var2":
    myVal = "value2";
    break;
  default:
    myVal = "value3";
}

// my_val evaluated to a specific value 
console.log(myVal);

Answer 1

您可以使用具有三进制的对象来设置默认值，如下所示：

const obj = {
  "var1":"value1",
  "var2":"value2",
  "defaultVal": "value3" // default value
},
getVal = sVar => sVar in obj ? obj[sVar] : obj["defaultVal"];

// Use case 1:
console.log(getVal("var1")); // get "var1" from the object

// Use case 2:
console.log(getVal("foo")); // get "foo" from the object, doesn't exsist, so we get the fault value

上面创建了一个对象，该对象中的每个键都指向一个值（即myVar应该变成什么）。如果myVar不在对象中，它将默认为defaultVal；如果它不在对象中，它将检索关联的值。

Answer 2

或者，如果仅返回值，则可以使用Map。

let map = new Map([["var1","value1"], ["var2", "value2"]])
const getVar = myVar => map.has(myVar) ? map.get(myVar) : "value3"

// Use

let myVar = 'var2'
myVar = getVar(myVar)
console.log(myVar)

Answer 3

您的代码有效：

let myVal = null;
let myVar = 'var1';

switch (myVar) {
  case "var1": 
    myVal = "value1";
    break;
  case "var2":
    myVal = "value2";
    break;
  default:
    myVal = "value3";
}

// my_val evaluated to a specific value 
console.log(myVal);

但是没有switch语句的一种更好的方法：

const obj = {
  var1: 'value1',
  var2: 'value2',
  default: 'value3'
};
const myVar = 'var1';
const myVal1 = obj[myVar] || obj.default;
const myVal2 = obj['asdfasdf'] || obj.default;

console.log(myVal1);
console.log(myVal2);

Answer 4

您可以使用&&中的Boolean Operators ||和Javascript来达到类似的目的：

let my_var = "var2";
let my_val =
(my_var === "var1" && "value1") ||
(my_var === "var2" && "value2") ||
"value3";

console.log(my_val);

let my_var2 = "var3";
let my_val2 =
(my_var2 === "var1" && "value1") ||
(my_var2 === "var2" && "value2") ||
"value3";

console.log(my_val2)

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侧面说明：此方法仅适用于原始Javascript值。让我们看一些方法失败的例子：

let my_var = [1,2,3];
let my_val =
(my_var === "var1" && "value1") ||
(my_var === [1,2,3] && "value2") ||
"value3";

console.log(my_val);

let my_var1 = {"a":"b"};
let my_val1 =
(my_var1 === "var1" && "value1") ||
(my_var1 === {"a":"b"} && "value2") ||
"value3";

console.log(my_val1);

let my_var2 = NaN;
let my_val2 =
(my_var2 === "var1" && "value1") ||
(my_var2 === NaN && "value2") ||
"value3";

console.log(my_val2);

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Ruby案例-vs JavaScript案例

4 个答案: