Excellent work

[JimCarnicelli]

Thank you for this. It works very well for me. I'm using it presently to process the US Census Department's 2020 census block shapes for each state:

https://www.census.gov/cgi-bin/geo/shapefiles/index.php?year=2024&layergroup=Blocks+%282020%29

I had to write code to fetch and unzip all the states' archives. I wanted the shapes and metadata about each. here's a look at what these blocks look like when opened in Google Earth Pro:

Here's the approach I'm taking to processing one state. I need one DBF, one SHX, and one SHP file:

const dbfFile = await loadFile(`${tempPath}/${sourceName}/${sourceName}.dbf`)
const shpFile = await loadFile(`${tempPath}/${sourceName}/${sourceName}.shp`)
const shxFile = await loadFile(`${tempPath}/${sourceName}/${sourceName}.shx`)
const dbfReader = await DbfReader.fromFile(dbfFile)
const shpReader = await ShapeReader.fromFile(shpFile, shxFile)
for (let i = 0; i < shpReader.recordCount; i++) {
    const dbf = dbfReader.readRecord(i)
    const geom = shpReader.readGeom(i)
    const geoJson = geom.toGeoJson() as GeoJsonPolygon
    const fields: any = {}
    dbfReader.fields.forEach((f, j) => {
        fields[f.name] = dbf[j]
    })

    // Your code for handling one census block goes here:
    console.log(fields, geoJson.coordinates)

}

The only challenge I had was in creating the loadFile() function. I used your on fileMock.ts code as a starting point:

export const loadFile = async (filePath: string): Promise<FileMock> => {
    const buf = await fs.promises.readFile(filePath)
    const ab = new ArrayBuffer(buf.length)
    const view = new Uint8Array(ab)
    for (let i = 0; i < buf.length; ++i) {
        view[i] = buf[i]
    }
    return new FileMock(ab)
}

class FileMock implements File {
    private _buf: ArrayBuffer

    constructor(buffer: ArrayBuffer) {
        this._buf = buffer
    }

    lastModified: number
    name: string
    webkitRelativePath: string
    size: number
    type: string
    bytes(): Promise<Uint8Array> {
        throw new Error('Method not implemented.')
    }
    slice(start?: number, end?: number, contentType?: string): Blob {
        throw new Error('Method not implemented.')
    }
    stream(): ReadableStream<Uint8Array> {
        throw new Error('Method not implemented.')
    }
    text(): Promise<string> {
        throw new Error('Method not implemented.')
    }

    public async arrayBuffer(): Promise<ArrayBuffer> {
        return this._buf
    }
}

No doubt I could have done this part in a more elegant way than I ultimately did. Consider adding handlers for file paths as strings if you decide to update this someday.

Thank you again for sharing!