As I transition from JavaScript to TypeScript, I have encountered a situation with filtering null values from an array. In JavaScript, I would typically use .filter(x => x) to achieve this. However, in TypeScript, it is asking me to specify that the array may contain null, even though the intention is to remove all instances of null from the array:
interface ILabels {
alias: string
publicKey: string
lat: number
long: number
}
const labels: ILabels[] = data.map((d) => {
if (d.lat && d.long) {
return {
alias: d.alias || d.publicKey,
publicKey: d.publicKey,
lat: d.lat,
long: d.long,
};
}
return null;
}).filter((x) => x);
I am wondering how I can communicate to TypeScript that there will not be any null values in this array. The error message thrown by TypeScript reads as follows:
TS2322: Type '({ alias: string; publicKey: string; lat: number; long: number; } | null)[]' is not assignable to type 'ILabels[]'. Type '{ alias: string; publicKey: string; lat: number; long: number; } | null' is not assignable to type 'ILabels'. Type 'null' is not assignable to type 'ILabels'.