如何让 JavaScript 评估一个字符串等等

Question

我决定用 JavaScript 做一个数学游戏，我对 JS 很陌生。我希望它从数组中选择一个随机操作并用两个随机数对其进行评估，但它不起作用。任何帮助表示赞赏。谢谢！

代码：

 var mathGame = function() {
     var operators = ["+", "-", "*", "/"];
     var operatorChoice = Math.floor((Math.random() * 4) + 1); 
     var points = 1;
     var numberOfQuestions = prompt("How many questions would you like?");
     var highestNumber = prompt("What is the highest number you would like to be quizzed on?");
     for (var i = 0; i < numberOfQuestions; i++) {
         var x = Math.floor((Math.random() * highestNumber) + 1);
         var y = Math.floor((Math.random() * highestNumber) + 1);
         var answer = (x operators[operatorChoice] y);
         var user_answer = prompt(x + operators[operatorChoice] + y);
         if (user_answer == answer) {
             alert("Yes!");
             points = points + 2;
         } else {
            if (points > 0) {
                points = points - 2;
            }
             alert("Sorry, that was incorrect, the answer is " + answer);
         }
     }
     alert("Your total points were " + points);
 };

Answer 1

你可以使用 eval：

var answer = eval(x + operators[operatorChoice] + y);

eval 通常不被接受，因为如果参数包含用户输入会很危险。但是由于您自己生成所有输入，并且它只包含列表中的数字和运算符，所以这是合理的使用它。

更好、更通用的处理方法是为每个操作定义函数并调用它们。

var mathGame = function() {
    function add(x, y) { return x + y; }
    function subtract(x, y) { return x - y; }
    function multiply(x, y) { return x * y; }
    function divide(x, y) { return x / y; }
    var operators = ["+", "-", "*", "/"];
    var operations = [add, subtract, multiply, divide];
    var operatorChoice = Math.floor(Math.random() * operators.length); 
    var points = 1;
    var numberOfQuestions = prompt("How many questions would you like?");
    var highestNumber = prompt("What is the highest number you would like to be quizzed on?");
    for (var i = 0; i < numberOfQuestions; i++) {
        var x = Math.floor((Math.random() * highestNumber) + 1);
        var y = Math.floor((Math.random() * highestNumber) + 1);
        var answer = operations[operatorChoice](x, y);
        var user_answer = prompt(x + operators[operatorChoice] + y);
        if (user_answer == answer) {
            alert("Yes!");
            points = points + 2;
        } else {
            if (points > 0) {
                points = points - 2;
            }
            alert("Sorry, that was incorrect, the answer is " + answer);
        }
    }
    alert("Your total points were " + points);
};
mathGame();

Yo 在您的代码中还有另一个错误。设置operatorChoice 时，不应将1 添加到随机数中。这会产生一个从1 到4 的数字，但operators 的索引是0 到3。