turf.featureOf

What is turf.featureOf?

turf.featureOf is a runtime assertion that throws an Error if a Feature's geometry type does not match a target string. It is used by Turf functions that expect a specific geometry and is exported for your own helpers.

turf.featureOf(feature, type, name) → void

Parameters:

• feature — the Feature to validate
• type — expected geometry type (e.g. 'Polygon')
• name — the caller's function name, included in the error

When would you use turf.featureOf?

Use turf.featureOf inside your own API surface when a function requires one geometry type — an area calculator that wraps turf.area but only accepts Polygons, or a routing helper that only accepts LineStrings. The thrown error mirrors the style of Turf core.

1function polygonPerimeter(feature) {
2  turf.featureOf(feature, 'Polygon', 'polygonPerimeter');
3  return turf.length(turf.polygonToLine(feature));
4}

FAQs

How do I install Turf.js to use this function?

Install npm install @turf/invariant and import import { featureOf } from '@turf/invariant', or use turf.featureOf from the umbrella bundle.

Does featureOf accept bare geometries?

No — it expects a Feature wrapper. Use turf.geojsonType or wrap the geometry with turf.feature before calling.

Can it accept multiple types?

No, type is a single string. Validate against multiple types with two calls inside a try/catch, or check the type manually.

When should I use featureOf vs collectionOf?

Use featureOf for a single Feature input. Use turf.collectionOf when every Feature in a FeatureCollection must match a type.