> [1, 2, 3] + [4, 5, 6] == "1, 2, 34, 5, 6" Well, `+` is a string operator. There's no infix array concatenation operator, so makes sense. > parseInt(0.000001

> [1, 2, 3] + [4, 5, 6] == "1, 2, 34, 5, 6" Well, `+` is a string operator. There's no infix array concatenation operator, so makes sense. > parseInt(0.000001) == 0 > parseInt(0.0000001) == 1 Never knew about this one! Quite funny actually and I'm curious why that happens. I suppose because `0.0000001` is represented as an exponent rather than a decimal? Although I haven't seen `parseInt` used since 2015, you should use `Number`. > "" + 5 == "5" > "" - 5 = -5 iirc `+` operator: - If LHS is a string, concatenate - Otherwise, cast to Number and perform arithmetic. `-` operator: - Perform arithmetic. All of these are explainable, and never catch anybody competent out in practice. And, since TypeScript is the norm in a lot of places now, it's never an issue.