Guide to making a GeoJSON Feature object with Typescript and react-leaflet

Attempting to generate a react element from a Feature in Typescript has been unsuccessful for me. (I'm utilizing react-leaflet + Typescript) With regular javascript, the process is as follows:

<Map
    {...}
    <GeoJSON 
        data={...} <- Here I insert my feature in JSON format
        style={...} <- Relevant style settings
     />
/>

However, when trying the exact same approach in Typescript, I face the following error:

No overload matches this call.
  Overload 1 of 2, '(props: Readonly<GeoJSONProps>): GeoJSON<GeoJSONProps, GeoJSON<any>>', provided the following error.
    Type '{ type: string; geometry: { type: string; coordinates: number[]; }; }' cannot be assigned to type 'GeoJsonObject'.
      Object literal can only specify known properties, and 'geometry' does not exist in type 'GeoJsonObject'.
  Overload 2 of 2, '(props: GeoJSONProps, context?: any): GeoJSON<GeoJSONProps, GeoJSON<any>>', provided the following error.
    Type '{ type: string; geometry: { type: string; coordinates: number[]; }; }' cannot be assigned to type 'GeoJsonObject'.
      Object literal can only specify known properties, and 'geometry' does not exist in type 'GeoJsonObject'.ts(2769)

I have attempted many variations, one of which looks like this:

<Map
    {...}
    <GeoJSON
        data={{
            type: "Feature",
            geometry: {
                type: "Point",
                coordinates: [125.6, 10.1]
            }
        }}
    />
/>

Upon inspecting the type definition of GeoJsonObject, it lacks the "geometry" field, only having the "type" field. How should I pass the geometry to the GeoJSON element I am creating? (type definition of GeoJsonObject: )

This code works in standard javascript, do you know why?

Answer №1

Preferred Solution

Ensure you use the appropriate data type for the GeoJson object you wish to work with.

import { GeoJSON } from 'react-leaflet';

const pointData: GeoJSON.Feature = {
    type: 'Feature',
    geometry: {
      type: 'Point',
      coordinates: [125.6, 10.1],
    },
    properties: {},
};

<Map
    {...}
    <GeoJSON data={pointData} />
/>

Alternate Solution (less recommended)

Instruct the Typescript compiler to recognize the object as of type GeoJsonObject.

import { GeoJsonObject } from 'geojson';

<Map
    {...}
    <GeoJSON
        data={{
            type: "Feature",
            geometry: {
                type: "Point",
                coordinates: [125.6, 10.1]
            }
        } as GeoJsonObject }
    />
/>

Answer №2

It appears that the issue lies with the code and typing of the GeoJSON element. It seems like the component is specifically looking for a GeoJsonObject and does not support the Feature. One potential solution could be to modify the type of the data property to Feature<Point> to see if that resolves the error.

Answer №3

Several things are going on in this scenario.

First and foremost, as per the @types/geojson type definitions, a point Feature must have its type field defined as a string literal type of "Feature" (while the geometry object requires its type field to be a string literal type of "Point").

Secondly, the TypeScript compiler fails to correctly infer that the "type" fields should possess the precise string literal types (instead, it assumes they are just general "string" types). A comprehensive explanation for this issue can be found in this answer provided in response to the question "Typescript - Why can't this string literal type be inferred?".

Now that we have identified the problem, it can be rectified. The following is an updated version of your example that should resolve the issue:

<Map
    {...}
    <GeoJSON
        data={{
            type: "Feature" as "Feature",
            geometry: {
                type: "Point" as "Point",
                coordinates: [125.6, 10.1]
            }
        }}
    />
/>

The only alteration made here is the inclusion of two type assertions: as "Feature" and as "Point", indicating to the TypeScript compiler that these "type:" fields should specifically have the string literal types "Feature" and "Point," respectively.

To avoid repetition, you also have the option of utilizing as const instead of as "Feature", etc.

Answer №4

It is highly likely that you are overlooking the properties member within your GeoJSON Feature object(s). Make sure to include it, even if it is just an empty object:

{
  type: "Feature",
  geometry: {
    type: "Point",
    coordinates: [125.6, 10.1]
  },
  properties: {} // This is required for a Feature object
}

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