successfully inject map d3 into target/index.html (correct branch this time!)

js/map.js

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+// Width and height
+var chart_width     =   1000;
+var chart_height    =   600;
+
+// Projection
+var projection = d3.geoMercator() //changing to geoAlbers makes the map disappear
+    .scale(1500)
+    .center([-91.34397, 32.25196])
+    .translate([chart_width / 2, chart_height / 2]);
+var path = d3.geoPath()
+    .projection(projection);
+
+// Create SVG
+var svg = d3.select("body")
+    .append("svg")
+    .attr("width", chart_width)
+    .attr("height", chart_height);
+
+var map = svg.append( 'g' )
+    .attr( 'id', 'map' );
+
+// Add map features
+d3.json('../cache/state_map.geojson', function(us_data){
+
+    map.selectAll( 'path' )
+        .data(us_data.features)
+        .enter()
+        .append('path')
+        .attr('d', path)
+        .attr('fill', "cornflowerblue")
+        .attr('stroke', '#fff')
+        .attr('stroke-width', 0.5)
+        .on("mouseover", mouseover)
+        .on("mouseout", mouseout);
+
+});
+
+function mouseover(d){
+  d3.select(this).style('fill', 'orange'); 
+}
+
+function mouseout(d){
+  d3.select(this).style('fill', "cornflowerblue");
+}

scripts/process/save_map.R

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+fetchTimestamp.save_map <- vizlab::alwaysCurrent
+
+#' Saves sf data as geojson.
+#' @description Converts sf data to sp, then saves as geojson for use in d3.
+#' 
+#' @param viz a vizlab object including \code{viewbox_limits} and \code{fetch_args}
+#' @details 
+#' Depends on: \code{map_data}: an sf representation of the x and y 
+#' (geographic coordinates) values of map_data shapes (counties, states, countries, etc).
+#'   
+process.save_map <- function(viz){
+  deps <- readDepends(viz)
+  checkRequired(deps, "map_data")
+  map_data <- deps[["map_data"]]
+
+  # spatial data needs to be sp to use writeOGR
+  # saves empty file if there is not any map features
+  if(nrow(map_data) > 0){
+    map_data_sp <- as(map_data, "Spatial") 
+    rgdal::writeOGR(map_data_sp, viz[['location']], 
+                    layer="map_data_sp", driver="GeoJSON")
+  } else {
+    write.table(data.frame(), viz[["location"]])
+  }
+
+}