如何在Typescript中声明可为空的对象文字变量？

Question

In typescript 2.2, when strictNullChecks option is true, how to declare a nullable object literal variable :

let myVar = { a: 1, b: 2 };
myVar = null; // Error can not assign null

The only ways I found is :

// Verbose
let myVar: { a: number; b: number; } | null  = { a: 1, b: 2 };

// Bad, same as having no type
let myVar: any| null  = { a: 1, b: 2 };

Answer 1

You can accomplish this by writing a nullable utility function:

const nullable = <T>(a: T) => a as T | null;

let myVar = nullable({ a: 1, b: 2 });
myVar = null; // Valid!

This does introduce an extra function call at variable initialization time, but likely this won't affect you much in most real world scenarios. The code is fairly clean, so I'm a fan of this solution.

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One other not so great way to do this would be the following:

const fake = { a: 1, b: 2 };
let realVar: typeof fake | null = fake;
realVar = null;

The downsides are as follows:

• The code is somewhat cryptic to those not very familiar with TypeScript
• You have an extra runtime variable assignment for no reason
• The code still isn't that concise