如何继续执行 JavaScript if.. else if 语句，直到收到有效输入？

Question

如何使用 if...else if 语句继续提示用户提供有效响应？我的脚本目前可以运行一次，但随后就会中断：

var enterNum = prompt("Please enter a number between 1 and 100", "");


if (isNaN(enterNum)){
    enterNum = prompt("You did not enter a valid number. Please try again", "")
}
else if (enterNum < 1 || enterNum >100){
    enterNum = prompt("Your number is not between 1 and 100. Please try again", "")
}
else{
    document.write("Your number is ", enterNum)
}

提前致谢！

Answer 1

var enterNum = prompt("Please enter a number between 1 and 100", "");

while(isNaN(enterNum) || enterNum < 1 || enterNum >100) {
    enterNum = prompt("You did not enter a valid number. Please try again", "")
}
document.write("Your number is ", enterNum)

Answer 2

var valid = false;
var msg = "Please enter a number between 1 and 100";

while(!valid){
    var enterNum = prompt(msg, "");

    if (isNaN(enterNum)){
        msg = "You did not enter a valid number. Please try again";
    }
    else if (enterNum < 1 || enterNum >100){
        msg = "Your number is not between 1 and 100. Please try again";
    }
    else{
        valid = true;
        document.write("Your number is ", enterNum)
    }
}

还有很多其他方法可以完成类似的事情，具体取决于风格。这是为了可读性。还可以消除 valid 变量，只需使用 while(true)，然后在输入正确后break。 document.write 也可能会在一段时间之后。

Answer 3

你不能只用 if/else。使用循环。例子：

var enterNum = prompt("Please enter a number between 1 and 100", "");
while(true)
{
  if (isNaN(enterNum)){
      enterNum = prompt("You did not enter a valid number. Please try again", "")
  }
  else if (enterNum < 1 || enterNum >100){
      enterNum = prompt("Your number is not between 1 and 100. Please try again", "")
  }
  else
    break;
}
document.write("Your number is ", enterNum)

Answer 4

使用 while 循环

http://help.dottoro.com/ljqepqhd.php#dowhile

或

http://help.dottoro.com/ljqepqhd.php#while

Answer 5

我讨厌 javascript，所以我的语法可能是关闭的，但类似：

var isValid = false;
var message = "Please enter a number between 1 and 100";

while(isValid == false)
{
    var enterNum = prompt(message, "");

    if (isNaN(enterNum)){
        isValid = false;
        message = "You did not enter a valid number. Please try again";
    }
    else if (enterNum < 1 || enterNum >100){
        isValid = false;
        message = "Your number is not between 1 and 100. Please try again";
    }
    else{
        isValid = true;
        document.write("Your number is ", enterNum)
    }
}

使用 do/while 循环可能会更整洁一些。