Null coalescing operator in React JS/ Typescript [duplicate]

Answer 1

This is a proposed feature in TypeScript, under the legendary Issue #16

It won't be introduced into TypeScript until the ECMAScript spec for this feature is firm as there is a desire for the TypeScript implementation to follow that specification - so you'll get it early, but not massively early in this case.

It is referred to as any of the following:

• Null Propagation Operator
• Existential Operator
• Null Coalesce Operator

Answer 2

Update in 2020: The nullish-coalescing operator mentioned below is now through the process and in ES2020, as is the optional chaining operator that lets you do:

let postal_code = address?.postal_code;
// −−−−−−−−−−−−−−−−−−−−−−^

With optional chaining, if address is null or undefined, postal_code will get undefined as its value. But if address is neither null nor undefined, postal_code will get the value of address.postal_code.

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JavaScript doesn't have a null-coalescing operator (nor does TypeScript, which mostly limits itself to adding a type layer and adopting features that are reasonably far along the path to making it into JavaScript). There is a proposal for a JavaScript null-coalescing operator, but it's only at Stage 1 of the process.

Using the && idiom you've described is a fairly common approach:

let postal_code = address && address.postal_code;

If address is null (or any other falsy¹ value), postal_code will be that same value; otherwise, it will be whatever value address.postal_code was.

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¹ The falsy values are 0, "", NaN, null, undefined, and of course false.