Question

So I have always wanted to do something like this, but never knew how to use an undefined natural variable (e.g. 1, 2, 3, 4, 5 …)

I want something like this:

if($("#container").width() == 400*n) {
  //do something
}

In which case n can be any natural cardinal number (and preferably not zero). How do you define n?

Answer 1

JavaScript does not solve equations with unknowns for you; at any given time, a variable always holds a specific value.

So, what you seem to want to do (if I understand your question correctly) is not possible. Instead, you need to solve the equation you gave yourself:

$("#container").width() == 400 * n

can be restated as

$("#container").width() / 400 == n

Now, since you require n to be an integer, the above statement means that dividing $("#container").width() will yield a whole number. The requirement “dividing a by x yields a whole number” is usually expressed with the modulo operator (% in JavaScript) as a % x == 0. Thus you end up with:

$("#container").width() % 400 == 0