How to test type of input into prompt for conditional statement - Javascript

Question

If i want write an if statement where on the web page a prompt for your username pops up and i want it to be a string only how do i do this. For example if you type in a string it would say "username accepted" but if you type in a number it would say "username denied". The code I have so far says Username Accepted everytime.

let webUser = prompt("Please create a username", "typehere");

if (webUser != null) {
  document.getElementById("root").innerHTML =
    "Hello " + webUser + "! How are you today?";
}

if (typeof webUser == 'string' || webUser instanceof String) {
  alert('Username Accepted')
} else {
  alert('Username Denied')
}

Prompt always returns a string. It will never return a number or null. — Jonas Wilms
– Jonas Wilms, Commented Mar 28, 2018 at 6:10

HardikS · Accepted Answer · 2018-03-28 05:51:06Z

1

If you want to implement without RegEx:

let webUser = prompt("Please create a username", "typehere");

if (webUser != null) {
	document.getElementById("root").innerHTML = "Hello " + webUser + "! How are you today?";
}

if (isNaN(+webUser)) {  
	alert('Username Accepted');
}
else {
	alert('Username Denied') ; 
}

<div id="root">

</div>

answered Mar 28, 2018 at 5:51

HardikS

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CertainPerformance · Accepted Answer · 2018-03-28 05:48:02Z

0

The type of value you get from a prompt will always be a string, even if it has numbers in it. If you want to check to see if a string consists of only numbers, you can use a regular expression:

const webUser = prompt("Please create a username", "typehere");
if (/^\d+$/.test(webUser.trim())) console.log('invalid');
else console.log('valid');

answered Mar 28, 2018 at 5:48

CertainPerformance

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Comments

intentionally-left-nil · Accepted Answer · 2018-03-28 06:13:27Z

0

prompt always returns a string data type. What you are trying to determine is whether that string is parseable as an integer. You can see some examples of how to do so here: how to parse string to int in javascript

edited Mar 28, 2018 at 6:13

answered Mar 28, 2018 at 5:49

intentionally-left-nil

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1 Comment

D. React Over a year ago

Thanks I’ll check it out

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