How to do prompt validation?

Question

JavaScript

How to check for an empty string (a space is also an empty string), for cancellation, for a number and for the number 0.
I can’t find the necessary information, or I’m not asking the right question.

Answer 1

let string = prompt(". . .", "")

// проверка на пустую строку (пробел - тоже пустая строка)
if (string.length === 0 || string === " ") . . .

// проверка на отмену (prompt() возвращает null, если была произведена отмена)
if (string === null) . . .

Further, you can do it yourself.