No-Library (pure JS), HTML, CSS, JavaScript
Use Number() function. If a string cannot be converted, the value returned is NaN. The isNaN() function allows to check for that.
Also an example of how using "return" statement turns a function into sort of a variable, and how a function can be passed as innerHTML!
The value entered in the prompt box becomes the value of that variable
The easiest example of recursion as a basic syntactic principle: you can assign a variable a new value calculated from its current value.
One of the important fundamental techniques in JavaScript programming