Simple Javascript prompt validation loop not working

Question

I cant seems to get this to work.

<script language="JavaScript">
var name = null;
do
{
    var name = prompt("Please enter your full name","");
}
while(name != null);
</script>

"" != null is true. You want while (name == null) (although I'd recommend name == "") — Bergi
– Bergi, Commented Jun 17, 2015 at 3:51

Arun P Johny · Accepted Answer · 2015-06-17 03:18:10Z

1

When you enter a blank string and press OK, it returns a empty string not null, null is returned only when you press cancel.

You can test for truthyness of the returned value

var name = null;
do {
  name = prompt("Please enter your full name");
  console.log(name)
}
while (!name);
console.log('done', name)

answered Jun 17, 2015 at 3:18

Arun P Johny

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Comments

Bradley Flood · Accepted Answer · 2015-06-17 03:25:01Z

0

I would use a boolean value:

var name = false;
do
{
    name = prompt("Please enter your full name",'');
}
while(!name); // While name is not true

Also you were re-declaring the name var again on within the do loop, remove the var in the loop.

answered Jun 17, 2015 at 3:25

Bradley Flood

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4 Comments

Bergi Over a year ago

Why introduce another type? Also, the redeclaration is not really a problem.

rellik Over a year ago

Thanks similarly how do i validate the input is a date? i cant seem to get .typeof to work

Bradley Flood Over a year ago

@Bergi Good point. I used a type to make the logic easier to understand, but does this have a performance cost? Might be worth it. As for calling var again, agreed this isn't a problem but it's still not necessary nor good practice IMO. Cheers

Bergi Over a year ago

Using false makes everything even more confusing. Now name is undefined before being initialised, then false, then either null or a string (depending on what prompt returned). I'm not talking about performance costs, but about best practises indeed.

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