Question

我试过添加一个Do / While循环，然后我尝试了一个If语句，但我似乎无法让它工作。

我正在尝试确定用户是否进行了三次猜测，并在userGuess提示符下点击取消..然后它会返回一个警报（＆＃34;你是一只鸡＆＃34;）; < / p>

//declare variables
var sportsArray = new Array("Football", "Basketball", "Rollerblading", "Hiking", "Biking", "Swimming");
var name = "";
var score = 0;
var loops = 0;


// prompts for user name, checks for input.
do {
    name = prompt("Enter your first name", "");
}
while (name == "");


for (loops = 1;loops <=3; loops++) {

    var sGuess = prompt("Enter a sport guess", "");
    // uses substrings to ultimately capitalize the 1st letter, and make everything after it lowerCase.
    var sFirstPart = sGuess.substr(0, 1);
    var sFirstCap = sFirstPart.toUpperCase();
    var sSecondPart = sGuess.substring(1, sGuess.length);
    var sSecondLow = sSecondPart.toLowerCase();
    // concats the two parts into one string
    var usableGuess = sFirstCap + sSecondLow;

    // if user hits cancel on the sGuess prompt
    if (sGuess == "") { 
        alert("You are a chicken");
    }

    // checks if usableGuess is contained in the arry or not.
    if (sportsArray.indexOf(usableGuess) === -1) { 
            document.write("Sorry! Try again.<br />");
            score = score -5;
        } 

        else { 
            document.write("You are good, try again.<br />"); 
            score = score + 5;
            }
    }
    //depending on the user score, prompts one of three messages.
    if (score < 0) { 
        document.write(name + ", you do not demonstrate ESP tendencies at this time.<br />");
        } else if (score < 15) { 
            document.write(name + ", you are not bad.<br />");
            } else { 
                document.write("<br/>" + name + ", you are a mind reader!<br />");
            }

Answer 1

提示返回null值，点击取消，因此substring()方法失败并显示错误（Uncaught TypeError: Cannot read property 'substr' of null）。

您需要在调用提示后立即检查，然后继续

  var sGuess = prompt("Enter a sport guess", "");
  if (sGuess == "") {
    alert("You are a chicken");
    continue;
  }

Answer 2

从以下地址更新sGuess：

if (sGuess == "") { 
        alert("You are a chicken");
}

到下一个：

if (sGuess == null) { 
        alert("You are a chicken");
}

如果用户点击取消sGuess等于null，则验证第三次用户尝试是否已取消，请按取消添加检查loops计数器值(sGuess == null && loops == 3)。

Answer 3

只需检查结果，看看是否提供了值：

 name = prompt("Enter your first name", "");

 // If no name value was received:
 if(!name){
      alert("Chicken!");
 }

Answer 4

如果用户点击取消，

“prompt”返回null。在这种情况下，所有substr和后续代码都将失败。

    var sGuess = prompt("Enter a sport guess", "");
    if(sGuess !== null) {
        // uses substrings to ultimately capitalize the 1st letter, and make everything after it lowerCase.
        var sFirstPart = sGuess.substr(0, 1);
        var sFirstCap = sFirstPart.toUpperCase();
        var sSecondPart = sGuess.substring(1, sGuess.length);
        var sSecondLow = sSecondPart.toLowerCase();
        // concats the two parts into one string
        var usableGuess = sFirstCap + sSecondLow;

    } else {
        // if user hits cancel on the sGuess prompt
        alert("You are a chicken");
    }

...

Answer 5

在这个特殊情况下，我最终选择了以下内容并完成了工作。

    // if user hits cancel on the sGuess prompt
    if (!sGuess && loops < 4) { 
        alert("You are a chicken");
    }

如果用户＆＃34;取消＆＃34;提示框然后

5 个答案: