假设您要运行if / else条件

Question

我正在尝试运行此代码以根据某些条件打印一个值，但它仅打印一个值。这是代码：

let instagramlikes;

let sitetraffic;

let dailytraffic;

function clientwidgets(x) {

  if (x === instagramlikes) {

    console.log("This is A");

  } else if (x === sitetraffic) {

    console.log("This is B");

  } else if (x === dailytraffic) {

    console.log("This is C")

  }

};

console.log(clientwidgets(instagramlikes));

console.log(clientwidgets(sitetraffic));

console.log(clientwidgets(dailytraffic));

Answer 1

从技术上讲， JavaScript没有枚举。如果不初始化变量，则将其初始化为未定义。也就是说，以下两个语句完全相同：let instagramlikes;let instagramlikes = undefined并且在您的函数中，您基本上传入x和undefined。如果这则检查x === instagramlikes其翻译为undefined === undefined，这将是true。为了模拟枚举，您可以尝试将变量设置为某个值，如下所示：const instagramlikes = 'instagramlikes';const sitetraffic = 'sitetraffic';const dailytraffic = 'dailytraffic';function clientwidgets(x) {  if (x === instagramlikes) {    return "This is A";  } else if (x === sitetraffic) {    return "This is B";  } else if (x === dailytraffic) {    return "This is C";  }};console.log(clientwidgets(instagramlikes));console.log(clientwidgets(sitetraffic));console.log(clientwidgets(dailytraffic));虽然它不一定是字符串，但是您可以使用数字或任何对象。如果您要定位的环境支持，则可以使用符号（例如Symbol）。Symbol的每个实例都是唯一的，因此与之进行的比较===应该完美无缺。const instagramlikes = Symbol();const sitetraffic = Symbol();const dailytraffic = Symbol();function clientwidgets(x) {  if (x === instagramlikes) {    return "This is A";  } else if (x === sitetraffic) {    return "This is B";  } else if (x === dailytraffic) {    return "This is C";  }};console.log(clientwidgets(instagramlikes));console.log(clientwidgets(sitetraffic));console.log(clientwidgets(dailytraffic));

Answer 2

尝试为每个不同的选项分配一个唯一的值。let instagramlikes = 1;let sitetraffic = 2;let dailytraffic = 3;function clientwidgets(x){  if (x === instagramlikes){    console.log("This is A");  } else if (x === sitetraffic){    console.log("This is B");  } else if (x === dailytraffic){    console.log("This is C")  }}clientwidgets(instagramlikes);clientwidgets(sitetraffic);clientwidgets(dailytraffic);我将创建一个对象枚举来也包含所有类型：const TYPE = {  INSTAGRAM_LIKES:1,  SITE_TRAFFIC:2,  DAILY_TRAFFIC:3}然后像这样打电话clientwidgets(TYPE.INSTAGRAM_LIKES);