为什么 React 条件渲染会渲染 NaN？

Question

Given value = NaN When value && value > 0 && <Component> .

For some reason, the app renders "NaN" rather than not rendering anything. Am I missing something? I would have thought that because NaN is not greater than 0...it would not render anything?

Answer 1

The logical AND ( && ) expression syntax is:

expr1 && expr2

According to the documentation:

If expr1 can be converted to true , returns expr2 ; else, returns expr1 .

Because NaN is expr1 and is falsy, NaN is returned.

If you want the component to render only if value exists and is a number greater than 0, you may be able to simply write:

value > 0 && <Component>

Answer 2

so you basically might give this a shot

if value !== NaN {
    if value && value > 0 && <Component> {
       // do something 
    } else {}
} else {}

or chain the entire logic, but personally I'd prefer this for readability