在收到有效输入之前，如何继续执行JavaScript if .. else if语句？

Question

How can I continue prompting a user for a valid response using if... else if statements? My script currently works once, but then breaks:

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)
}

Thanks in advance!

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

You can't with only if/else. Use a loop. Example:

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 3

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)
    }
}

There are a bunch of other ways to do a similar thing, somewhat depending on style. This went for readability. Could also eliminate the valid variable and simply have while(true) then break once the input is correct. The document.write could also be after the while.

Answer 4

use a while loop instead

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

or

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

Answer 5

I hate javascript so my syntax is probably off but something like:

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)
    }
}

Using a do/while loop might be a little neater.