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I know what a ternary operator is in React.

When I'm developing a React Native app I encounter this kind of syntax that is covered by my ESLint as an unexpected token:

ESLint: Parsing error: Unexpected token .

It goes like this:

const routeName = route.state?.routes[route.state.index]?.name ?? INITIAL_ROUTE_NAME;

What does that mean? It uses null coalescing operator in the end, however, I can't understand what the question mark does before a dot.

I know it is the correct syntax because it is a template from expo and they're very popular in the React Native development community.

Can anyone help me explain?

DᴀʀᴛʜVᴀᴅᴇʀ
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Robert Tirta
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1 Answers1

142

That's optional chaining: MDN

The optional chaining operator (?.) enables you to read the value of a property located deep within a chain of connected objects without having to check that each reference in the chain is valid.

The ?. operator is like the . chaining operator, except that instead of causing an error if a reference is nullish (null or undefined), the expression short-circuits with a return value of undefined. When used with function calls, it returns undefined if the given function does not exist.

This results in shorter and simpler expressions when accessing chained properties when the possibility exists that a reference may be missing. It can also be helpful while exploring the content of an object when there's no known guarantee as to which properties are required.

NULL SWEΔT
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