Loop that prompts user until valid input [closed]

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Closed 3 years ago.

Question: How to continuously prompt user when age is invalid (below 0 above 200, or not-a-number)?

var userAge = prompt("Please enter your age");
while (isNaN(userAge)){
    alert("That's not a number, please retry.");
    var userAge = prompt("Please re-enter your age.");
}

if (userAge == 0){
    alert("So you're a baby!");
}
while( userAge < 0  || userAge >= 200){
    alert("I think you may be lying about your age.");
    var userAge = prompt("Please re-enter your age, don't lie this time.");
    {continue}
}

if (userAge > 0 || userAge < 200){
    alert("That's a good age."); 
}

</script>

回答1:

You can return from while loop with break statement. For example:

var userAge = prompt("Please enter your age");
while (true) {
    if (isNaN(userAge)) {
        alert("That's not a number, please retry.");
    } else if (userAge < 0 || userAge >= 200) {
        alert("I think you may be lying about your age.");
    } else {
        break;
    }
    var userAge = prompt("Please re-enter your age.");
}
if (userAge == 0) {
    alert("So you're a baby!");
} else {
    alert("That's a good age.");
}

来源：https://stackoverflow.com/questions/35044961/loop-that-prompts-user-until-valid-input