Null coalescing operator in React JS/ Typescript [

问题:

This question already has an answer here:

• Typescript the safe navigation operator ( ?. ) or (!.) and null property paths 4 answers
• Replacement of Elvis Operator of Angular2 in Typescript 2 answers

We have the Null coalescing operator in .NET and we can use as below

string postal_code = address?.postal_code;

Same thing can we do in React JS?

What i found like we can do with && operator

in address.ts file

string postal_code = address && address.postal_code;

what i need like .net feature is possible in typescript with react JS, is that possible ?

something like:

string postal_code = address?.postal_code // I am getting the error in this line if I try to use like .NET

回答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

回答2:

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.