How to check null value?[SOLVED]

Question

If the prompt is empty how could I check the value if it is null?
Using if condition.

Answer 1

The easiest way is:

var val = prompt('Hello');
if(val){
alert('Not null');
}
else {
alert('Null');
}

This code works because if the input value is empty, it converts to boolean false. Otherwise it converts to boolean true.

For whitespace, it behaves same as val != null checking.

Answer 2

this function will return true if val is empty, null, undefined, false, the number 0 or NaN. You are a bit overdoing it. To check if a variable is not given a value, you would only need to check against undefined and null. This is assuming 0 , "" , and objects(even empty object and array) are valid "values".

//i think my answer will help you😉😁

Answer 3

The prompt() method returns String. If the user clicks "OK", the input value is returned. If the user clicks "cancel", null is returned. If the user clicks OK without entering any text, an empty string is returned.

source: https://www.w3schools.com/jsref/met_win_prompt.asp

Checking for an empty string.
https://www.w3schools.com/code/tryit.asp?filename=G2AN4FX57NDN

Answer 4

let ans = prompt('Question?')
if(ans !== null && ans.trim()){
alert('not empty')
} else {
alert('empty')
}

Answer 5

Sarthak

An Empty string and null will convert to 0, so you would have to check for 0.

https://www.w3schools.com/js/js_type_conversion.asp
There is a chart on conversion at the bottom of the page, that make an excellent reference for type conversion

Answer 6

Max Andal Prompt takes only string inputs.
So, "0" === 0 // false
Thus the only possible inputs to come is either a string or empty value.
Strings are truthy and empty or null is falsy.
So, Adnan Zawad Toky 's solution holds true.
And also thanks to ODLNT for helping me