I am trying to discern the difference between: if else and else if How do you use these? And when do you use them and when not?
No true, because with such syntax else if is side-effect (i.e. it comes for free). In other words there is no else if syntax, there is only if and else here.
5 Как такового оператора else if нет, это лишь использование ещё одного if в ветке else другого if. Но разница между ними есть.
"One option is to code the else clause—with a null statement if necessary—to show that the else case has been considered. Coding null elses just to show that that case has been considered might be overkill, but at the very least, take the else case into account.
In your case, whether you need an else clause depends on whether you want specific code to run if and only if neither of condition1, condition2, and condition3 are true. else can be omitted for any if statement, there is nothing special in the last if of an if / else if chain. This is documented in any JavaScript grammar, e.g. in the specification.
Do I need a last else clause in an if...else if statement?
Então sim, no seu exemplo você deve fazer escolher o else if principalmente por questão de semântica. Mas isto não é algo bobo que só serve para atender uma regra.
IF, ELSE IF, ELSE ou IF IF IF. Quando usar, qual a diferença?