The type undefined gets added to custom dataset properties.

[u840903]

We type our custom graphs like this...

import type { ChartDataset } from "chart.js";

declare module "chart.js" {
  interface ChartTypeRegistry {
    customLine: ChartTypeRegistry["line"] & {
      datasetOptions: {
        id: string;
      };
    };
  }
}

const getId = (dataset:ChartDataset<"customLine">) => {
  return dataset.id // (property) id?: string | undefined
}

..but when we look at customLine datasets, the id can be a string or undefined. How can we get rid of the undefined type?

Typescript Playground
https://www.typescriptlang.org/play/?ts=5.3.3#code/JYWwDg9gTgLgBDAnmApnA3nAwgCwIawAieMeAzivAL5wBmUEIcARAMb6wB0AVmcwNwAoQQBMUrADYE0ICCICuEtGw4wefDILhxgAOxgootPKzS4CMACrIUAJRQBzYGRhREm7dtbyXjADJ6KABc2KrWqPZOLm4A2swSgcwAunAAZB6e2iIk5JQA8mAwwBC6ZCHoWpmewCIh0XoOQlVwVE2erZVUgl2CrCUucA6UAJIicAC8cAAU2aQUMEHmRDnzADxsPjD+iQB8AJQTOxlQlPJQunCzuWo1cAD0d9NgDKiwiAc1APx1rg1wAD5weS6MS0QIibpAA