checking a variable value using an OR operator

Question

So, a junior programmer on my team today wrote the following piece of code:

if(status === (\"incomplete\" || \"unknown\"))

Which is obvious

Answer 1

But what I can't explain is why exactly status === ("incomplete" || "unknown") wouldn't work

That's because the expression in the parenthesis is evaluated first. The non-empty string incomplete is truthy, so the OR-expression ("incomplete" || "unknown") yields "incomplete" and only that is then compared with your status variable.

To shorten the condition, there are many ways including arrays of values, regular expression test etc.