Leaflet Map as Elixir Phoenix LiveView Component

README.md

Note

This was just a quick copy/paste of snippets from a project.

I dod not get to test this version yet.

app.js

// Add this to your app.js phoenix application

let Hooks = {}

Hooks.Map = {
  mounted(){
    const markers = {}
    const map = L.map('mapid').setView([51.505, -0.09], 14)
    const paths = {}
    let geojsonLayer = L.geoJSON().addTo(map).setStyle({color: "#6435c9"})

    L.tileLayer('https://api.mapbox.com/styles/v1/{id}/tiles/{z}/{x}/{y}?access_token={accessToken}', {
        attribution: 'Map data &copy; <a href="https://www.openstreetmap.org/copyright">OpenStreetMap</a> contributors, Imagery © <a href="https://www.mapbox.com/">Mapbox</a>',
        maxZoom: 18,
        id: 'mapbox/streets-v11',
        tileSize: 512,
        zoomOffset: -1,
        accessToken: YOUR_MAPBOX_ACCESS_TOKEN
    }).addTo(map)

    this.handleEvent("update_marker_position", ({reference, lat, lon, center_view}) => {
      markers[reference].setLatLng(L.latLng(lat, lon))

      if (center_view) {
        map.flyTo(L.latLng(lat, lon))
      }
    })
    
    this.handleEvent("draw_path", ({reference, coordinates, color}) => {
      data = {
        "type": "LineString",
        "coordinates": coordinates
      }

      geojsonLayer.addData(data)
    })

    this.handleEvent("view_init", ({reference, lat, lon, zoom_level = 20}) => {
      geojsonLayer.remove()

      geojsonLayer = L.geoJSON().addTo(map).setStyle({color: "#6435c9"})

      map.setView(L.latLng(lat, lon), zoom_level)
    })

    this.handleEvent("set_zoom_level", ({zoom_level}) => {
      map.setZoom(zoom_level)
    })

    this.handleEvent("add_marker", ({reference, lat, lon}) => {      
      // lets not add duplicates for the same marker!
      if (markers[reference] == null) {
        const marker = L.marker(L.latLng(lat, lon))

        marker.addTo(map)

        markers[reference] = marker
      }
    })

    this.handleEvent("add_marker_with_popup", ({reference, lat, lon, link}) => {      
      // lets not add duplicates for the same marker!
      if (markers[reference] == null) {
        const marker = L.marker(L.latLng(lat, lon))

        marker.bindPopup(`<a href=\"${link}\">${reference}</a>`)

        marker.addTo(map)

        markers[reference] = marker
      }
    })

    this.handleEvent("clear", () => {
      geojsonLayer.remove()

      geojsonLayer = L.geoJSON().addTo(map)

      for (const [reference, value] of Object.entries(markers)) {
        marker = markers[reference]

        marker.remove()

        markers.delete(reference)
      }

    })

    this.handleEvent("remove_marker", ({reference}) => {
      if (markers[reference] != null) {
        marker = markers[reference]

        marker.remove()

        markers.delete(reference)
      }

      geojsonLayer.remove()
    })
  }
}

LeafletMap.ex

defmodule Components.LeafletMap do
  use Phoenix.Component

  attr :class, :string, default: nil

  def map(assigns) do
    ~H"""
    <div style="overflow: hidden" phx-update="ignore" id="mapcontainer">
        <div class={@class} phx-hook="Map" id="mapid"></div>
    </div>
    """
  end

  # might be off if the maps shape is not close to a square.
  def calculate_initial_map_zoom_level(n, e, s, w) do
    lat_to_radiant = fn lat ->
      sin = :math.sin(lat * :math.pi() / 180)
      radX2 = :math.log((1 + sin) / (1 - sin)) / 2
      max(min(radX2, :math.pi()), -:math.pi()) / 2
    end

    lat_difference = abs(lat_to_radiant.(n) - lat_to_radiant.(s))
    lon_difference = abs(e - w)

    lat_fraction = lat_difference / :math.pi()
    lon_fraction = lon_difference / 360

    # Ensure we never get 0 in division. 1.0e-5 was chosen arbitrarily after trying different values.
    lat_zoom = :math.log(1 / max(lat_fraction, 1.0e-5)) / :math.log(2)
    lon_zoom = :math.log(1 / max(lon_fraction, 1.0e-5)) / :math.log(2)

    # Slight zoom out for vertical dimension, because our map view is very wide and not square.
    min(lat_zoom - 0.5, lon_zoom)
    |> min(20) # Lets not zoom in to infinity
  end

  def liveview_setup_map(socket, opts \\ []) do
    socket
    |> assign(selected_address: address)
    |> Phoenix.LiveView.push_event("view_init", %{
      reference: opts[:reference],
      lat: opts[:latitude],
      lon: opts[:longitude],
      zoom_level: opts[:zoom_level] || 15
    })
    |> Phoenix.LiveView.push_event("add_marker", %{
      reference: opts[:reference],
      lat: opts[:latitude],
      lon: opts[:longitude]
    })
    |> Phoenix.LiveView.push_event("update_marker_position", %{
      reference: opts[:reference],
      lat: address[:latitude],
      lon: address[:longitude],
      center_view: true
    })
  end
end

map_live.ex

defmodule MyAppWeb.MapLive do
  use MyAppWeb, :live_view

  @impl true
  def mount(%{"id" => id}, _session, socket) do
    opts = [latitude: 51.123456, longitude: 7.123456, reference: "main"]
  
    LeafletMap.liveview_set_map_to_address(socket, opts)
  end
  
  @impl true
  def render(assigns) do
    ~H"""
      <div class="h-screen bg-gray-100">
        <div class="flex h-screen justify-center items-center rounded-md shadow-lg">
          <LeafletMap.map class="h-80" />
        </div>
      </div>
    """
  end
end

Great approach to get leaflet working in Elixir!

I spent some time getting this to work: The biggest time consumer was to discover that the flex class in line 15 of map_live would render the map gray. Anyways, here is what else i changed to make it run

• Removed address variable in liveview_setup_map (looked like some left overs)
• Called liveview_setup_map instead of liveview_set_map_to_address in map_live.ex
• Added leaflet CSS and JS imports to <head> in root.html.heex from hosted source https://leafletjs.com/download.html
• Added alias Components.LeafletMap, as: LeafletMap to map_live.ex
• Added the hooks to livesocket in app.js by altering this line:

let liveSocket = new LiveSocket("/live", Socket, {params: {_csrf_token: csrfToken}, hooks: Hooks})

@nomtrosk right, sorry for rushing it out like this, but glad you got it to work in the end!

If someone else is struggling with this, I’ve outlined a straightforward approach that works without extra customization. However, since the hook can be highly dependent on individual project needs, I don’t think creating a Hex package is justified.
Simbolismo-Digital/prever@aae7c2d
Tip: remember running mix assets.setup