TypeScript Map: Type 'number | undefined' is not assignable to type 'number'-CodePudding

I have the typescript code below in VS Code,

const hash: Map<string, number> = new Map<string, number>([
    ['Small', 1],
    ['Medium', 2],
    ['Large', 3],
]);
const sz = 'Small';
const num: number = hash.has(sz) ? hash.get(sz) : 0;

It keeps complaining:

Type 'number | undefined' is not assignable to type 'number'. Type 'undefined' is not assignable to type 'number'.

Not sure anything I did wrong here. Doesn't hash.has(sz) already ensure hash.get(sz) won't be undefined?

My current approach is to use const num: number = hash.has(sz) ? hash.get(sz)! : 0; but it doesn't seem to be a graceful to me.

What's the proper way to fix this kind of issue?

CodePudding user response：

const hash: Map<string, number> = new Map<string, number>([
    ['Small', 1],
    ['Medium', 2],
    ['Large', 3],
]);
const sz = 'Small';
const num: number = hash.get(sz) ?? 0;

This should do it. Map.prototype.get returns undefined if it can't find the key, which we can null coalesce into 0.

CodePudding user response：

Try removing the comma from the 3rd element of the array: ['Large', 3]