@turf/invariant

What is @turf/invariant?

@turf/invariant is a module within the Turf.js library that provides utility functions for validating and extracting GeoJSON objects. It ensures that the input data conforms to the expected GeoJSON format, which is crucial for performing various geospatial operations.

What are @turf/invariant's main functionalities?

getCoord

The `getCoord` function extracts the coordinates from a GeoJSON Point feature. This is useful when you need to work directly with the coordinates of a point.

const turf = require('@turf/invariant');
const point = { type: 'Feature', geometry: { type: 'Point', coordinates: [102.0, 0.5] } };
const coord = turf.getCoord(point);
console.log(coord); // [102.0, 0.5]

getCoords

The `getCoords` function extracts the coordinates from a GeoJSON LineString or Polygon feature. This is useful for accessing the array of coordinates that make up the geometry.

const turf = require('@turf/invariant');
const line = { type: 'Feature', geometry: { type: 'LineString', coordinates: [[102.0, 0.0], [103.0, 1.0]] } };
const coords = turf.getCoords(line);
console.log(coords); // [[102.0, 0.0], [103.0, 1.0]]

getGeom

The `getGeom` function extracts the geometry object from a GeoJSON feature. This is useful when you need to work with the geometry independently of the feature properties.

const turf = require('@turf/invariant');
const feature = { type: 'Feature', geometry: { type: 'Polygon', coordinates: [[[102.0, 0.0], [103.0, 1.0], [104.0, 0.0], [102.0, 0.0]]] } };
const geom = turf.getGeom(feature);
console.log(geom); // { type: 'Polygon', coordinates: [[[102.0, 0.0], [103.0, 1.0], [104.0, 0.0], [102.0, 0.0]]] }

getType

The `getType` function returns the type of a GeoJSON object. This is useful for validating the type of geometry you are working with.

const turf = require('@turf/invariant');
const feature = { type: 'Feature', geometry: { type: 'Polygon', coordinates: [[[102.0, 0.0], [103.0, 1.0], [104.0, 0.0], [102.0, 0.0]]] } };
const type = turf.getType(feature);
console.log(type); // 'Polygon'

Other packages similar to @turf/invariant

geojson-validation

The `geojson-validation` package provides functions to validate GeoJSON objects against the GeoJSON specification. It is similar to @turf/invariant in that it ensures the input data conforms to the expected GeoJSON format, but it focuses more on validation rather than extraction of specific components.

geojson-utils

The `geojson-utils` package offers a set of utility functions for working with GeoJSON data, including validation, distance calculations, and bounding box operations. It provides broader functionality compared to @turf/invariant, which is more focused on validation and extraction.

README

@turf/invariant

getCoord

Unwrap a coordinate from a Feature with a Point geometry, a Point geometry, or a single coordinate.

Parameters

• obj Any any value

Returns Array<number> a coordinate

geojsonType

Enforce expectations about types of GeoJSON objects for Turf.

Parameters

• value GeoJSON any GeoJSON object

• type string expected GeoJSON type

• name string name of calling function

• Throws Error if value is not the expected type.

featureOf

Enforce expectations about types of Feature inputs for Turf. Internally this uses geojsonType to judge geometry types.

Parameters

• feature Feature a feature with an expected geometry type

• type string expected GeoJSON type

• name string name of calling function

• Throws Error error if value is not the expected type.

collectionOf

Enforce expectations about types of FeatureCollection inputs for Turf. Internally this uses geojsonType to judge geometry types.

Parameters

• featurecollection FeatureCollection a featurecollection for which features will be judged

• type string expected GeoJSON type

• name string name of calling function

• Throws Error if value is not the expected type.

---

This module is part of the Turfjs project, an open source module collection dedicated to geographic algorithms. It is maintained in the Turfjs/turf repository, where you can create PRs and issues.

Installation

Install this module individually:

$ npm install @turf/invariant

Or install the Turf module that includes it as a function:

$ npm install @turf/turf