Javascript - 获取切换案例中的案例数 [英] Javascript - get number of cases in switch case

问题描述

是否可以在 Javascript 中获取 switch case 语句中的 case 数?

Is it possible to get the number of cases in a switch case statement in Javascript?

所以对于这样的事情

showError: function (status) {
        var message = '';

        //If the error comes from the browser's routing sys (the event parameter is the failed route), default to a 404 error
        if (typeof status === 'string') {
            status = 404;
        }

        //Determines the appropriate error message
        switch (status) {
            case 404:
                message = 'the page could not be found'; 
                break;

            case 500:
                message = 'internal server error';
                break; 
        }

        //Renders the view-less error template
        region.show(new Backbone.View());
        region.el.innerHTML = Marionette.TemplateCache.get(TemplIds.error)({message: message});
    },

推荐答案

在 javascript 中 switch 和 case 是关键字逻辑操作符，没有原型或者可以通过JavaScript 引擎.但是，functions 是动态对象，因此如果将 switch 语句放在函数中，则可以在该函数上调用 toString() 来评估函数的内容，如下所示:

In javascript switch and case are keyword logical operators and do not have a prototype or are introspectable by the javascript engine. However, functions are dynamic objects so if you put a switch statement within a function, then you can call toString() on that function to evaluate the function's contents like this:

var fn = function(value){
  switch(value){
    case "A": 
      return "Apple";
    case "B":
      return "Banana";
  }
};

var fnToString = fn.toString();
var fnBody = fnToString.match(/function[^{]+\{([\s\S]*)\}$/)[1];
var count = fnBody.match(/case/g).length; //should equal 2

注意:正则表达式容易出错，但可以为您提供策略要点.我会让你喜欢正则表达式，以找出单词 case 出现的次数.

Note: The regex is error prone, but gives you a gist of the strategy. I'll let you get fancy with the regex to find out how many times the word case occurs.

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