Types and Conversion

typeof tells you what kind of value you have: "number", "string", "boolean", "object" or "undefined". Convert on purpose with Number("42"), String(42) and Boolean(value). JavaScript also converts automatically in some places, which surprises people: "5" * 2 is 10, but "5" + 2 is "52". The values 0, "", null, undefined and NaN are falsy; everything else is truthy.

How it reads

• Number("sky") cannot convert, so it gives NaN (not a number)
• * always does maths, but + joins text if either side is a string
• Empty text and 0 are falsy, so Boolean("") is false

Cloud tip: Convert input explicitly with Number(...) as soon as you receive it, instead of relying on automatic conversion later.