openlayers2 geojson to geometry

ol2-json-utils.ts

import ol = require("ol2");

export type GeoJsonGeometry = {
    type: "point";
    coordinates: number[];
} | {
    type: "multipoint";
    coordinates: number[][];
} | {
    type: "linestring";
    coordinates: number[][];
} | {
    type: "multilinestring";
    coordinates: number[][][];
} | {
    type: "polygon";
    coordinates: number[][][];
} | {
    type: "multipolygon";
    coordinates: number[][][][];
};

export function fromJson(json: GeoJsonGeometry) {
    switch (json.type) {
        case "point":
            return new ol.Geometry.Point(json.coordinates[0], json.coordinates[1]);
        case "multipoint":
            return new ol.Geometry.MultiPoint(json.coordinates.map(p => new ol.Geometry.Point(p[0], p[1])));
        case "linestring":
            return new ol.Geometry.LineString(json.coordinates.map(p => new ol.Geometry.Point(p[0], p[1])));
        case "multilinestring":
            return new ol.Geometry.MultiLineString(json.coordinates.map(l => new ol.Geometry.LineString(l.map(p => new ol.Geometry.Point(p[0], p[1])))));
        case "polygon":
            return new ol.Geometry.Polygon(json.coordinates.map(l => new ol.Geometry.LineString(l.map(p => new ol.Geometry.Point(p[0], p[1])))));
        case "multipolygon":
            return new ol.Geometry.MultiPolygon(json.coordinates.map(polygon => new ol.Geometry.Polygon(polygon.map(l => new ol.Geometry.LineString(l.map(p => new ol.Geometry.Point(p[0], p[1])))))));
    }
}