How to use the relateurl.PATH_RELATIVE function in relateurl

import { map } from 'ix/iterable'
import RelateUrl from 'relateurl'
import { URL } from 'url'

/**
 * Options to make sure that RelateUrl only outputs relative URLs and performs not other "smart" modifications.
 * They would mess up things like prefix checking.
 */
const RELATE_URL_OPTIONS: RelateUrl.Options = {
    // Make sure RelateUrl does not prefer root-relative URLs if shorter
    output: RelateUrl.PATH_RELATIVE,
    // Make sure RelateUrl does not remove trailing slash if present
    removeRootTrailingSlash: false,
    // Make sure RelateUrl does not remove default ports
    defaultPorts: {},
}

/**
 * Like `path.relative()` but for URLs.
 * Inverse of `url.resolve()` or `new URL(relative, base)`.
 */
export const relativeUrl = (from: URL, to: URL): string => RelateUrl.relate(from.href, to.href, RELATE_URL_OPTIONS)

/**
 * A Map of URIs to values.
 */
export class URLMap implements Map {

public insert(element: lsif.Vertex | lsif.Edge): void {
        if (element.type === lsif.ElementTypes.vertex) {
            switch (element.label) {
                case lsif.VertexLabels.metaData:
                    this.handleMetaData(element)
                    break

                case lsif.VertexLabels.document: {
                    if (!this.projectRoot) {
                        throw new Error('No metadata defined.')
                    }

                    const path = RelateUrl.relate(this.projectRoot.href + '/', new URL(element.uri).href, {
                        defaultPorts: {},
                        output: RelateUrl.PATH_RELATIVE,
                        removeRootTrailingSlash: false,
                    })

                    this.documentPaths.set(element.id, path)
                    this.containsData.set(element.id, new Set())
                    break
                }

                // The remaining vertex handlers stash data into an appropriate map. This data
                // may be retrieved when an edge that references it is seen, or when a document
                // is finalized.

                case lsif.VertexLabels.range:
                    this.rangeData.set(element.id, {
                        startLine: element.start.line,
                        startCharacter: element.start.character,