How to check input in prompt for empty string or space in javascript?

Question

JavaScript

Sorry for the stupid question)
By analogy with checking for NaN

if (isNaN(a)) {
        alert('Это - не число!');
        continue;

you need to check for an empty string and a space. How can this be done? Thank you.

Answer 1

if (a === '')
  alert('Пустая строка')
if (a === ' ')
  alert('Это пробел')

Answer 2

if(!a.trim())
    alert('Строка пустая или состоит только из пробелов')

In my example, two features are used:

• The empty string boolean value is negative (false)
  
• The trim method is used to remove spaces from the beginning and end of a string. Remove spaces in variable with space = get empty string = get false