While loop - JavaScript

Question

let age = "";

while (age !== NaN) {

  age = prompt("what is your age");

  Number(age);

}

I can not leave the while loop although I write a number in the prompt box, why?

You initialize age to a string, and the return value from prompt() is also always a string, and no string is ever === to NaN. The call to Number(age) has no effect; you probably want age = Number(age);. — Pointy
– Pointy, Commented Dec 11, 2018 at 14:24

Mamun · Accepted Answer · 2018-12-11 16:19:00Z

4

You can use isNaN() function to determine whether a value is NaN or not. You have to add age == "" as part of the condition with || to pass for the initial value (empty string).

The condition should be:

while (isNaN(age) || age == "")

You also have to re-assign the converted value to the variable.

let age = "";
while (isNaN(age) || age === "") {
  age = prompt("what is your age");
  if(age == null)
    break;
  else
   age = Number(age);
}

edited Dec 11, 2018 at 16:19

answered Dec 11, 2018 at 14:28

Mamun

69k9 gold badges51 silver badges62 bronze badges

Sign up to request clarification or add additional context in comments.

6 Comments

H.A.A Over a year ago

let age = ""; while (isNaN(age) || age == "") { age = prompt("what is your age"); age = Number(age); } is a good solution. But whats is wrong with age === "" (with 3 equal signs). I leave the loop when I click Cancel or OK without writing. let age = ""; while (isNaN(age) || age === "") { age = prompt("what is your age"); age = Number(age); }

Mamun Over a year ago

@H.A.A, when cancel button is clicked age has null value, in that case you have to break the loop.....updated the answer....please check.

H.A.A Over a year ago

I got it. age = Number(age); changes the type of age to Number that is why age==="" does not work because empty "" is not a number.

H.A.A Over a year ago

The following code solved my problem: let age = ""; while (isNaN(age) || age == "") { age = prompt("what is your age"); age = Number(age); } let age = ""; while (isNaN(age) || age === "") { age = prompt("what is your age"); if(age == null) break; else age = Number(age); } leaves tho loop without asking the age again.

Mamun Over a year ago

@H.A.A, does my answer solve your question or you want some thing else?

|

Collectives™ on Stack Overflow

While loop - JavaScript

1 Answer 1

6 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

6 Comments

Your Answer

Sign up or log in

Post as a guest

Related