Question

I’m new to javascript, it must be very basic:

if (controllerName === ('about' || 'contact' || 'lessons')) {
        res.render(controllerName + '.ejs', locals);
    }

Only when controllerName=='about' I go inside, the rest of the cases I don’t.

How do the or and === operate in this case ?

Answer 1

You structured it incorrectly. A fix would be

if (controllerName == 'about' || controllerName == 'contact' || controllerName == 'lessons') {
    res.render(controllerName + '.ejs', locals);
}

The problem was that ('about' || 'contact' || 'lessons') evaluates to about since it is the first non-(null/undefined) value in the set. It seems like you want to compare controllerName to all three values so notice how my version of your code compares controllerName to all three values separately.