Loading a local .kml file using google maps?

The KML can't be accessed since it's on your local machine and google can't access that since it doesn't know how to get to localhost:8080

Unfortunately you cannot use "localhost". You have two choices:

1. place the kml on a publically available domain. (if google cannot access it, it won't work)
2. Use geoxml3 which basically does what google does but allows you to downlaod and host the parser JS file youself. It will allow you to load a LOCALHOST KML and parse it out for you (objects accessible via JSON) (http://code.google.com/p/geoxml3/).

Choice #1 might not be an option for those working on defense contracts and deal with sensitive information as the kml is sent to google in the background and rendered on the map.

This website, display-kml.appspot.com, requires that you copy/paste the entire KML file into the website. Alternatively, you can use Dropbox to host the KML file using your public folder. Within the public Dropbox folder, there is a right-click context menu that allows you to copy the URL.

The appspot website has a history of being unstable. As of January 2019, the website appears to be working.

1. http://display-kml.appspot.com/
2. https://www.dropbox.com/

Definitely, Google Maps KmlLayer is designed for you to send your data to them. https://developers.google.com/maps/documentation/javascript/kml

Have a look the following log.

//console
var src = 'https://developers.google.com/maps/documentation/javascript/examples/kml/westcampus.kml';

var kmlLayer = new google.maps.KmlLayer(src, {
  suppressInfoWindows: true,
  preserveViewport: false,
  map: your_gmap_object
});

Creating Marker, Polygon, they are all browser side parsing and rendering.

As you can see from next network log, KmlLayer class send source URL to Google Server to parse it and (do something in their end) and send the parsed result back to your browser to render.

//REQUEST from browser

https://maps.googleapis.com/maps/api/js/KmlOverlayService.GetOverlays?1shttps%3A%2F%2Fdevelopers.google.com%2Fmaps%2Fdocumentation%2Fjavascript%2Fexamples%2Fkml%2Fwestcampus.kml&callback=_xdc_._lidt3k&key=AIzaSyBeLTP20qMgxsQFz1mwLlzNuhrS5xD_a_U&token=103685

//RESPONSE from google server

/**/_xdc_._lidt3k && _xdc_._lidt3k( [0,"kml:cXOw0bjKUSmlnTN2l67v0Sai6WfXhSSWuyNaDD0mAzh6xfi2fYnBo78Y2Eg","|ks:;dc:tg;ts:51385071|kv:3|api:3",...
["KmlFile"],[[37.423017,-122.0927],[37.424194,-122.091498]],[["g74cf1503d602f2e5"],["g58e8cf8fd6da8d29"],["ge39d22e72437b02e"]],1,[["client","2"]],-21505,[["ks",";dc:tg;ts:51385071"],["kv","3"],["api","3"]]] )

As @capdragon mentioned above, it would be better parse KML by yourself.

UPDATE

Here is compact KML parser code. This only for google.maps Marker and Polygon.

html

<input type='file' accept=".kml,.kmz" onchange="fileChanged()">

script, I used typescript but it is pretty same with javascript

  file: any
  fileChanged(e) {
    this.file = e.target.files[0]
    this.parseDocument(this.file)
  }
  parseDocument(file) {
    let fileReader = new FileReader()
    fileReader.onload = async (e: any) => {
      let result = await this.extractGoogleCoords(e.target.result)

      //CREATE MARKER OR POLYGON WITH result here
      console.log(result)

    }
    fileReader.readAsText(file)
  }

  async extractGoogleCoords(plainText) {
    let parser = new DOMParser()
    let xmlDoc = parser.parseFromString(plainText, "text/xml")
    let googlePolygons = []
    let googleMarkers = []

    if (xmlDoc.documentElement.nodeName == "kml") {

      for (const item of xmlDoc.getElementsByTagName('Placemark') as any) {
        let placeMarkName = item.getElementsByTagName('name')[0].childNodes[0].nodeValue.trim()
        let polygons = item.getElementsByTagName('Polygon')
        let markers = item.getElementsByTagName('Point')

        /** POLYGONS PARSE **/        
        for (const polygon of polygons) {
          let coords = polygon.getElementsByTagName('coordinates')[0].childNodes[0].nodeValue.trim()
          let points = coords.split(" ")

          let googlePolygonsPaths = []
          for (const point of points) {
            let coord = point.split(",")
            googlePolygonsPaths.push({ lat: +coord[1], lng: +coord[0] })
          }
          googlePolygons.push(googlePolygonsPaths)
        }

        /** MARKER PARSE **/    
        for (const marker of markers) {
          var coords = marker.getElementsByTagName('coordinates')[0].childNodes[0].nodeValue.trim()
          let coord = coords.split(",")
          googleMarkers.push({ lat: +coord[1], lng: +coord[0] })
        }
      }
    } else {
      throw "error while parsing"
    }

    return { markers: googleMarkers, polygons: googlePolygons }

  }

output

markers: Array(3)
0: {lat: 37.42390182131783, lng: -122.0914977709329}
...

polygons: Array(1)
0: Array(88)
0: {lat: -37.79825999283025, lng: 144.9165994157198}
...