diff --git a/main.js b/main.js
index 6e06fb1c..17447830 100644
--- a/main.js
+++ b/main.js
@@ -128,9 +128,23 @@ let color = d3.scaleSequential(d3.interpolateSpectral); // default color scheme
 const lineGen = d3.line().curve(d3.curveBasis); // d3 line generator with default curve interpolation
 
 // d3 zoom behavior
-let scale = 1,
-  viewX = 0,
-  viewY = 0;
+let scale = 1;
+let viewX = 0;
+let viewY = 0;
+
+const zoomThrottled = throttle(doWorkOnZoom, 100);
+function zoomed() {
+  const {k, x, y} = d3.event.transform;
+
+  const isScaleChanged = Boolean(scale - k);
+  const isPositionChanged = Boolean(viewX - x || viewY - y);
+
+  scale = k;
+  viewX = x;
+  viewY = y;
+
+  zoomThrottled(isScaleChanged, isPositionChanged);
+}
 const zoom = d3.zoom().scaleExtent([1, 20]).on("zoom", zoomed);
 
 // default options
@@ -414,30 +428,24 @@ function showWelcomeMessage() {
   });
 }
 
-function zoomed() {
-  const transform = d3.event.transform;
-  const scaleDiff = scale - transform.k;
-  const positionDiff = (viewX - transform.x) | (viewY - transform.y);
-  if (!positionDiff && !scaleDiff) return;
+function doWorkOnZoom(isScaleChanged, isPositionChanged) {
+  viewbox.attr("transform", `translate(${viewX} ${viewY}) scale(${scale})`);
 
-  scale = transform.k;
-  viewX = transform.x;
-  viewY = transform.y;
-  viewbox.attr("transform", transform);
+  if (isPositionChanged) drawCoordinates();
 
-  // update grid only if view position
-  if (positionDiff) drawCoordinates();
-
-  // rescale only if zoom is changed
-  if (scaleDiff) {
+  if (isScaleChanged) {
     invokeActiveZooming();
     drawScaleBar();
   }
 
   // zoom image converter overlay
-  const canvas = document.getElementById("canvas");
-  if (canvas && +canvas.style.opacity) {
-    const img = document.getElementById("image");
+  if (customization === 1) {
+    const canvas = document.getElementById("canvas");
+    if (!canvas || canvas.style.opacity === "0") return;
+
+    const img = document.getElementById("imageToConvert");
+    if (!img) return;
+
     const ctx = canvas.getContext("2d");
     ctx.clearRect(0, 0, canvas.width, canvas.height);
     ctx.setTransform(scale, 0, 0, scale, viewX, viewY);
diff --git a/modules/ui/heightmap-editor.js b/modules/ui/heightmap-editor.js
index 7c8cf5b1..053dc477 100644
--- a/modules/ui/heightmap-editor.js
+++ b/modules/ui/heightmap-editor.js
@@ -131,15 +131,8 @@ function editHeightmap() {
 
   // Exit customization mode
   function finalizeHeightmap() {
-    if (viewbox.select("#heights").selectAll("*").size() < 200) {
-      tip("Insufficient land area! There should be at least 200 land cells to finalize the heightmap", null, "error");
-      return;
-    }
-
-    if (document.getElementById("imageConverter").offsetParent) {
-      tip("Please exit the Image Conversion mode first", null, "error");
-      return;
-    }
+    if (viewbox.select("#heights").selectAll("*").size() < 200) return tip("Insufficient land area! There should be at least 200 land cells to finalize the heightmap", null, "error");
+    if (document.getElementById("imageConverter").offsetParent) return tip("Please exit the Image Conversion mode first", null, "error");
 
     delete window.edits; // remove global variable
     redo.disabled = templateRedo.disabled = true;
@@ -1103,6 +1096,10 @@ function editHeightmap() {
       const reader = new FileReader();
 
       const img = new Image();
+      img.id = "imageToConvert";
+      img.style.display = "none";
+      document.body.appendChild(img);
+
       img.onload = function () {
         const ctx = document.getElementById("canvas").getContext("2d");
         ctx.drawImage(img, 0, 0, graphWidth, graphHeight);
@@ -1295,10 +1292,7 @@ function editHeightmap() {
     }
 
     function applyConversion() {
-      if (colorsAssigned.childElementCount < 3) {
-        tip("Please do the assignment first", false, "error");
-        return;
-      }
+      if (colorsAssigned.childElementCount < 3) return tip("Please do the assignment first", false, "error");
 
       viewbox
         .select("#heights")
@@ -1324,6 +1318,9 @@ function editHeightmap() {
       const canvas = document.getElementById("canvas");
       if (canvas) canvas.remove();
 
+      const image = document.getElementById("imageToConvert");
+      if (image) image.remove();
+
       d3.select("#imageConverter").selectAll("div.color-div").remove();
       colorsAssigned.style.display = "none";
       colorsUnassigned.style.display = "none";
diff --git a/modules/utils.js b/modules/utils.js
index afe22287..0194a1ff 100644
--- a/modules/utils.js
+++ b/modules/utils.js
@@ -11,11 +11,11 @@ function getBoundaryPoints(width, height, spacing) {
   const numberY = Math.ceil(h / bSpacing) - 1;
   let points = [];
   for (let i = 0.5; i < numberX; i++) {
-    let x = Math.ceil(w * i / numberX + offset);
+    let x = Math.ceil((w * i) / numberX + offset);
     points.push([x, offset], [x, h + offset]);
   }
   for (let i = 0.5; i < numberY; i++) {
-    let y = Math.ceil(h * i / numberY + offset);
+    let y = Math.ceil((h * i) / numberY + offset);
     points.push([offset, y], [w + offset, y]);
   }
   return points;
@@ -24,7 +24,7 @@ function getBoundaryPoints(width, height, spacing) {
 // get points on a regular square grid and jitter them a bit
 function getJitteredGrid(width, height, spacing) {
   const radius = spacing / 2; // square radius
-  const jittering = radius * .9; // max deviation
+  const jittering = radius * 0.9; // max deviation
   const jitter = () => Math.random() * 2 * jittering - jittering;
 
   let points = [];
@@ -40,7 +40,7 @@ function getJitteredGrid(width, height, spacing) {
 
 // return cell index on a regular square grid
 function findGridCell(x, y) {
-  return Math.floor(Math.min(y / grid.spacing, grid.cellsY -1)) * grid.cellsX + Math.floor(Math.min(x / grid.spacing, grid.cellsX-1));
+  return Math.floor(Math.min(y / grid.spacing, grid.cellsY - 1)) * grid.cellsX + Math.floor(Math.min(x / grid.spacing, grid.cellsX - 1));
 }
 
 // return array of cell indexes in radius on a regular square grid
@@ -55,14 +55,12 @@ function findGridAll(x, y, radius) {
     while (r > 1) {
       let cycle = frontier.slice();
       frontier = [];
-      cycle.forEach(function(s) {
-
-        c[s].forEach(function(e) {
+      cycle.forEach(function (s) {
+        c[s].forEach(function (e) {
           if (found.indexOf(e) !== -1) return;
           found.push(e);
           frontier.push(e);
         });
-
       });
       r--;
     }
@@ -100,7 +98,7 @@ function getGridPolygon(i) {
 
 // mbostock's poissonDiscSampler
 function* poissonDiscSampler(x0, y0, x1, y1, r, k = 3) {
-  if (!(x1 >= x0) || !(y1 >= y0) || !(r > 0)) throw new Error;
+  if (!(x1 >= x0) || !(y1 >= y0) || !(r > 0)) throw new Error();
 
   const width = x1 - x0;
   const height = y1 - y0;
@@ -113,8 +111,8 @@ function* poissonDiscSampler(x0, y0, x1, y1, r, k = 3) {
   const queue = [];
 
   function far(x, y) {
-    const i = x / cellSize | 0;
-    const j = y / cellSize | 0;
+    const i = (x / cellSize) | 0;
+    const j = (y / cellSize) | 0;
     const i0 = Math.max(i - 2, 0);
     const j0 = Math.max(j - 2, 0);
     const i1 = Math.min(i + 3, gridWidth);
@@ -134,14 +132,14 @@ function* poissonDiscSampler(x0, y0, x1, y1, r, k = 3) {
   }
 
   function sample(x, y) {
-    queue.push(grid[gridWidth * (y / cellSize | 0) + (x / cellSize | 0)] = [x, y]);
+    queue.push((grid[gridWidth * ((y / cellSize) | 0) + ((x / cellSize) | 0)] = [x, y]));
     return [x + x0, y + y0];
   }
 
   yield sample(width / 2, height / 2);
 
   pick: while (queue.length) {
-    const i = Math.random() * queue.length | 0;
+    const i = (Math.random() * queue.length) | 0;
     const parent = queue[i];
 
     for (let j = 0; j < k; ++j) {
@@ -171,20 +169,19 @@ function isWater(i) {
 }
 
 // convert RGB color string to HEX without #
-function toHEX(rgb){
-  if (rgb.charAt(0) === "#") {return rgb;}
+function toHEX(rgb) {
+  if (rgb.charAt(0) === "#") {
+    return rgb;
+  }
   rgb = rgb.match(/^rgba?[\s+]?\([\s+]?(\d+)[\s+]?,[\s+]?(\d+)[\s+]?,[\s+]?(\d+)[\s+]?/i);
-    return (rgb && rgb.length === 4) ? "#" +
-    ("0" + parseInt(rgb[1],10).toString(16)).slice(-2) +
-    ("0" + parseInt(rgb[2],10).toString(16)).slice(-2) +
-    ("0" + parseInt(rgb[3],10).toString(16)).slice(-2) : '';
+  return rgb && rgb.length === 4 ? "#" + ("0" + parseInt(rgb[1], 10).toString(16)).slice(-2) + ("0" + parseInt(rgb[2], 10).toString(16)).slice(-2) + ("0" + parseInt(rgb[3], 10).toString(16)).slice(-2) : "";
 }
 
 // return array of standard shuffled colors
 function getColors(number) {
-  const c12 = ["#dababf","#fb8072","#80b1d3","#fdb462","#b3de69","#fccde5","#c6b9c1","#bc80bd","#ccebc5","#ffed6f","#8dd3c7","#eb8de7"];
+  const c12 = ["#dababf", "#fb8072", "#80b1d3", "#fdb462", "#b3de69", "#fccde5", "#c6b9c1", "#bc80bd", "#ccebc5", "#ffed6f", "#8dd3c7", "#eb8de7"];
   const cRB = d3.scaleSequential(d3.interpolateRainbow);
-  const colors = d3.shuffle(d3.range(number).map(i => i < 12 ? c12[i] : d3.color(cRB((i-12)/(number-12))).hex()));
+  const colors = d3.shuffle(d3.range(number).map(i => (i < 12 ? c12[i] : d3.color(cRB((i - 12) / (number - 12))).hex())));
   return colors;
 }
 
@@ -193,30 +190,42 @@ function getRandomColor() {
 }
 
 // mix a color with a random color
-function getMixedColor(color, mix = .2, bright = .3) {
+function getMixedColor(color, mix = 0.2, bright = 0.3) {
   const c = color && color[0] === "#" ? color : getRandomColor(); // if provided color is not hex (e.g. harching), generate random one
   return d3.color(d3.interpolate(c, getRandomColor())(mix)).brighter(bright).hex();
 }
 
 // conver temperature from °C to other scales
 function convertTemperature(c) {
-  switch(temperatureScale.value) {
-    case "°C": return c + "°C";
-    case "°F": return rn(c * 9 / 5 + 32) + "°F";
-    case "K": return rn(c + 273.15) + "K";
-    case "°R": return rn((c + 273.15) * 9 / 5) + "°R";
-    case "°De": return rn((100 - c) * 3 / 2) + "°De";
-    case "°N": return rn(c * 33 / 100) + "°N";
-    case "°Ré": return rn(c * 4 / 5) + "°Ré";
-    case "°Rø": return rn(c * 21 / 40 + 7.5) + "°Rø";
-    default: return c + "°C";
+  switch (temperatureScale.value) {
+    case "°C":
+      return c + "°C";
+    case "°F":
+      return rn((c * 9) / 5 + 32) + "°F";
+    case "K":
+      return rn(c + 273.15) + "K";
+    case "°R":
+      return rn(((c + 273.15) * 9) / 5) + "°R";
+    case "°De":
+      return rn(((100 - c) * 3) / 2) + "°De";
+    case "°N":
+      return rn((c * 33) / 100) + "°N";
+    case "°Ré":
+      return rn((c * 4) / 5) + "°Ré";
+    case "°Rø":
+      return rn((c * 21) / 40 + 7.5) + "°Rø";
+    default:
+      return c + "°C";
   }
 }
 
 // random number in a range
 function rand(min, max) {
   if (min === undefined && max === undefined) return Math.random();
-  if (max === undefined) {max = min; min = 0;}
+  if (max === undefined) {
+    max = min;
+    min = 0;
+  }
   return Math.floor(Math.random() * (max - min + 1)) + min;
 }
 
@@ -245,7 +254,9 @@ function rn(v, d = 0) {
 
 // round string to d decimals
 function round(s, d = 1) {
-   return s.replace(/[\d\.-][\d\.e-]*/g, function(n) {return rn(n, d);})
+  return s.replace(/[\d\.-][\d\.e-]*/g, function (n) {
+    return rn(n, d);
+  });
 }
 
 // corvent number to short string with SI postfix
@@ -279,52 +290,50 @@ function capitalize(string) {
 
 // transform string to array [translateX,translateY,rotateDeg,rotateX,rotateY,scale]
 function parseTransform(string) {
-  if (!string) {return [0,0,0,0,0,1];}
-  const a = string.replace(/[a-z()]/g, "").replace(/[ ]/g, ",").split(",");
+  if (!string) {
+    return [0, 0, 0, 0, 0, 1];
+  }
+  const a = string
+    .replace(/[a-z()]/g, "")
+    .replace(/[ ]/g, ",")
+    .split(",");
   return [a[0] || 0, a[1] || 0, a[2] || 0, a[3] || 0, a[4] || 0, a[5] || 1];
 }
 
 // findAll d3.quandtree search from https://bl.ocks.org/lwthatcher/b41479725e0ff2277c7ac90df2de2b5e
-void function addFindAll() {
-  const Quad = function(node, x0, y0, x1, y1) {
+void (function addFindAll() {
+  const Quad = function (node, x0, y0, x1, y1) {
     this.node = node;
     this.x0 = x0;
     this.y0 = y0;
     this.x1 = x1;
     this.y1 = y1;
-  }
+  };
 
-  const tree_filter = function(x, y, radius) {
+  const tree_filter = function (x, y, radius) {
     var t = {x, y, x0: this._x0, y0: this._y0, x3: this._x1, y3: this._y1, quads: [], node: this._root};
-    if (t.node) {t.quads.push(new Quad(t.node, t.x0, t.y0, t.x3, t.y3))};
+    if (t.node) {
+      t.quads.push(new Quad(t.node, t.x0, t.y0, t.x3, t.y3));
+    }
     radiusSearchInit(t, radius);
 
     var i = 0;
-    while (t.q = t.quads.pop()) {
+    while ((t.q = t.quads.pop())) {
       i++;
 
       // Stop searching if this quadrant can’t contain a closer node.
-      if (!(t.node = t.q.node)
-          || (t.x1 = t.q.x0) > t.x3
-          || (t.y1 = t.q.y0) > t.y3
-          || (t.x2 = t.q.x1) < t.x0
-          || (t.y2 = t.q.y1) < t.y0) continue;
+      if (!(t.node = t.q.node) || (t.x1 = t.q.x0) > t.x3 || (t.y1 = t.q.y0) > t.y3 || (t.x2 = t.q.x1) < t.x0 || (t.y2 = t.q.y1) < t.y0) continue;
 
       // Bisect the current quadrant.
       if (t.node.length) {
         t.node.explored = true;
         var xm = (t.x1 + t.x2) / 2,
-            ym = (t.y1 + t.y2) / 2;
+          ym = (t.y1 + t.y2) / 2;
 
-        t.quads.push(
-          new Quad(t.node[3], xm, ym, t.x2, t.y2),
-          new Quad(t.node[2], t.x1, ym, xm, t.y2),
-          new Quad(t.node[1], xm, t.y1, t.x2, ym),
-          new Quad(t.node[0], t.x1, t.y1, xm, ym)
-        );
+        t.quads.push(new Quad(t.node[3], xm, ym, t.x2, t.y2), new Quad(t.node[2], t.x1, ym, xm, t.y2), new Quad(t.node[1], xm, t.y1, t.x2, ym), new Quad(t.node[0], t.x1, t.y1, xm, ym));
 
         // Visit the closest quadrant first.
-        if (t.i = (y >= ym) << 1 | (x >= xm)) {
+        if ((t.i = ((y >= ym) << 1) | (x >= xm))) {
           t.q = t.quads[t.quads.length - 1];
           t.quads[t.quads.length - 1] = t.quads[t.quads.length - 1 - t.i];
           t.quads[t.quads.length - 1 - t.i] = t.q;
@@ -334,29 +343,32 @@ void function addFindAll() {
       // Visit this point. (Visiting coincident points isn’t necessary!)
       else {
         var dx = x - +this._x.call(null, t.node.data),
-            dy = y - +this._y.call(null, t.node.data),
-            d2 = dx * dx + dy * dy;
+          dy = y - +this._y.call(null, t.node.data),
+          d2 = dx * dx + dy * dy;
         radiusSearchVisit(t, d2);
       }
     }
     return t.result;
-  }
+  };
   d3.quadtree.prototype.findAll = tree_filter;
 
-  var radiusSearchInit = function(t, radius) {
+  var radiusSearchInit = function (t, radius) {
     t.result = [];
-    t.x0 = t.x - radius, t.y0 = t.y - radius;
-    t.x3 = t.x + radius, t.y3 = t.y + radius;
+    (t.x0 = t.x - radius), (t.y0 = t.y - radius);
+    (t.x3 = t.x + radius), (t.y3 = t.y + radius);
     t.radius = radius * radius;
-  }
+  };
 
-  var radiusSearchVisit = function(t, d2) {
+  var radiusSearchVisit = function (t, d2) {
     t.node.data.scanned = true;
     if (d2 < t.radius) {
-      do {t.result.push(t.node.data); t.node.data.selected = true;} while (t.node = t.node.next);
+      do {
+        t.result.push(t.node.data);
+        t.node.data.selected = true;
+      } while ((t.node = t.node.next));
     }
-  }
-}()
+  };
+})();
 
 // get segment of any point on polyline
 function getSegmentId(points, point, step = 10) {
@@ -366,23 +378,23 @@ function getSegmentId(points, point, step = 10) {
   let minSegment = 1;
   let minDist = Infinity;
 
-  for (let i=0; i < points.length-1; i++) {
+  for (let i = 0; i < points.length - 1; i++) {
     const p1 = points[i];
-    const p2 = points[i+1];
+    const p2 = points[i + 1];
 
     const length = Math.sqrt(d2(p1, p2));
     const segments = Math.ceil(length / step);
     const dx = (p2[0] - p1[0]) / segments;
     const dy = (p2[1] - p1[1]) / segments;
 
-    for (let s=0; s < segments; s++) {
+    for (let s = 0; s < segments; s++) {
       const x = p1[0] + s * dx;
       const y = p1[1] + s * dy;
       const dist2 = d2(point, [x, y]);
 
       if (dist2 >= minDist) continue;
       minDist = dist2;
-      minSegment = i+1;
+      minSegment = i + 1;
     }
   }
 
@@ -418,7 +430,9 @@ function vowel(c) {
 
 // remove vowels from the end of the string
 function trimVowels(string) {
-  while (string.length > 3 && vowel(last(string))) {string = string.slice(0,-1);}
+  while (string.length > 3 && vowel(last(string))) {
+    string = string.slice(0, -1);
+  }
   return string;
 }
 
@@ -427,7 +441,7 @@ function getAdjective(string) {
   // special cases for some suffixes
   if (string.length > 8 && string.slice(-6) === "orszag") return string.slice(0, -6);
   if (string.length > 6 && string.slice(-4) === "stan") return string.slice(0, -4);
-  if (P(.5) && string.slice(-4) === "land") return string + "ic";
+  if (P(0.5) && string.slice(-4) === "land") return string + "ic";
   if (string.slice(-4) === " Guo") string = string.slice(0, -4);
 
   // don't change is name ends on suffix
@@ -436,16 +450,16 @@ function getAdjective(string) {
   if (string.slice(-1) === "i") return string;
 
   const end = string.slice(-1); // last letter of string
-  if (end === "a") return string += "n";
-  if (end === "o") return string = trimVowels(string) + "an";
-  if (vowel(end) || end === "c") return string += "an"; // ceiuy
-  if (end === "m" || end === "n") return string += "ese";
-  if (end === "q") return string += "i";
+  if (end === "a") return (string += "n");
+  if (end === "o") return (string = trimVowels(string) + "an");
+  if (vowel(end) || end === "c") return (string += "an"); // ceiuy
+  if (end === "m" || end === "n") return (string += "ese");
+  if (end === "q") return (string += "i");
   return trimVowels(string) + "ian";
 }
 
 // get ordinal out of integer: 1 => 1st
-const nth = n => n+(["st","nd","rd"][((n+90)%100-10)%10-1]||"th");
+const nth = n => n + (["st", "nd", "rd"][((((n + 90) % 100) - 10) % 10) - 1] || "th");
 
 // get two-letters code (abbreviation) from string
 function abbreviate(name, restricted = []) {
@@ -453,8 +467,8 @@ function abbreviate(name, restricted = []) {
   const words = parsed.split(" ");
   const letters = words.join("");
 
-  let code = words.length === 2 ? words[0][0]+words[1][0] : letters.slice(0,2);
-  for (let i = 1; i < letters.length-1 && restricted.includes(code); i++) {
+  let code = words.length === 2 ? words[0][0] + words[1][0] : letters.slice(0, 2);
+  for (let i = 1; i < letters.length - 1 && restricted.includes(code); i++) {
     code = letters[0] + letters[i].toUpperCase();
   }
   return code;
@@ -463,7 +477,7 @@ function abbreviate(name, restricted = []) {
 // conjunct array: [A,B,C] => "A, B and C"
 function list(array) {
   if (!Intl.ListFormat) return array.join(", ");
-  const conjunction = new Intl.ListFormat(window.lang || "en", {style:"long", type:"conjunction"});
+  const conjunction = new Intl.ListFormat(window.lang || "en", {style: "long", type: "conjunction"});
   return conjunction.format(array);
 }
 
@@ -472,7 +486,10 @@ function splitInTwo(str) {
   const half = str.length / 2;
   const ar = str.split(" ");
   if (ar.length < 2) return ar; // only one word
-  let first = "", last = "",  middle = "", rest = "";
+  let first = "",
+    last = "",
+    middle = "",
+    rest = "";
 
   ar.forEach((w, d) => {
     if (d + 1 !== ar.length) w += " ";
@@ -501,10 +518,10 @@ function ra(array) {
 function rw(object) {
   const array = [];
   for (const key in object) {
-    for (let i=0; i < object[key]; i++) {
+    for (let i = 0; i < object[key]; i++) {
       array.push(key);
     }
-  };
+  }
   return array[Math.floor(Math.random() * array.length)];
 }
 
@@ -515,33 +532,55 @@ function lim(v) {
 
 // get number from string in format "1-3" or "2" or "0.5"
 function getNumberInRange(r) {
-  if (typeof r !== "string") {ERROR && console.error("The value should be a string", r); return 0;}
+  if (typeof r !== "string") {
+    ERROR && console.error("The value should be a string", r);
+    return 0;
+  }
   if (!isNaN(+r)) return ~~r + +P(r - ~~r);
   const sign = r[0] === "-" ? -1 : 1;
   if (isNaN(+r[0])) r = r.slice(1);
   const range = r.includes("-") ? r.split("-") : null;
-  if (!range) {ERROR && console.error("Cannot parse the number. Check the format", r); return 0;}
+  if (!range) {
+    ERROR && console.error("Cannot parse the number. Check the format", r);
+    return 0;
+  }
   const count = rand(range[0] * sign, +range[1]);
-  if (isNaN(count) || count < 0) {ERROR && console.error("Cannot parse number. Check the format", r); return 0;}
+  if (isNaN(count) || count < 0) {
+    ERROR && console.error("Cannot parse number. Check the format", r);
+    return 0;
+  }
   return count;
 }
 
 // helper function non-used for the generation
 function drawCellsValue(data) {
   debug.selectAll("text").remove();
-  debug.selectAll("text").data(data).enter().append("text")
-    .attr("x", (d,i) => pack.cells.p[i][0]).attr("y", (d,i) => pack.cells.p[i][1]).text(d => d);
+  debug
+    .selectAll("text")
+    .data(data)
+    .enter()
+    .append("text")
+    .attr("x", (d, i) => pack.cells.p[i][0])
+    .attr("y", (d, i) => pack.cells.p[i][1])
+    .text(d => d);
 }
 
 // helper function non-used for the generation
 function drawPolygons(data) {
-  const max = d3.max(data), min = d3.min(data), scheme = getColorScheme();
+  const max = d3.max(data),
+    min = d3.min(data),
+    scheme = getColorScheme();
   data = data.map(d => 1 - normalize(d, min, max));
 
   debug.selectAll("polygon").remove();
-  debug.selectAll("polygon").data(data).enter().append("polygon")
-    .attr("points", (d,i) => getPackPolygon(i))
-    .attr("fill", d => scheme(d)).attr("stroke", d => scheme(d));
+  debug
+    .selectAll("polygon")
+    .data(data)
+    .enter()
+    .append("polygon")
+    .attr("points", (d, i) => getPackPolygon(i))
+    .attr("fill", d => scheme(d))
+    .attr("stroke", d => scheme(d));
 }
 
 // polyfill for composedPath
@@ -552,56 +591,86 @@ function getComposedPath(node) {
   else if (node.defaultView) parent = node.defaultView;
   if (parent !== undefined) return [node].concat(getComposedPath(parent));
   return [node];
-};
+}
 
 // polyfill for replaceAll
 if (!String.prototype.replaceAll) {
-  String.prototype.replaceAll = function(str, newStr){
-    if (Object.prototype.toString.call(str).toLowerCase() === '[object regexp]') return this.replace(str, newStr);
-    return this.replace(new RegExp(str, 'g'), newStr);
+  String.prototype.replaceAll = function (str, newStr) {
+    if (Object.prototype.toString.call(str).toLowerCase() === "[object regexp]") return this.replace(str, newStr);
+    return this.replace(new RegExp(str, "g"), newStr);
   };
 }
 
 // get next unused id
 function getNextId(core, i = 1) {
-  while (document.getElementById(core+i)) i++;
+  while (document.getElementById(core + i)) i++;
   return core + i;
 }
 
-function debounce(f, ms) {
+function debounce(func, ms) {
   let isCooldown = false;
 
-  return function() {
+  return function () {
     if (isCooldown) return;
-    f.apply(this, arguments);
+    func.apply(this, arguments);
     isCooldown = true;
-    setTimeout(() => isCooldown = false, ms);
+    setTimeout(() => (isCooldown = false), ms);
   };
 }
 
+function throttle(func, ms) {
+  let isThrottled = false;
+  let savedArgs;
+  let savedThis;
+
+  function wrapper() {
+    if (isThrottled) {
+      savedArgs = arguments;
+      savedThis = this;
+      return;
+    }
+
+    func.apply(this, arguments);
+    isThrottled = true;
+
+    setTimeout(function () {
+      isThrottled = false;
+      if (savedArgs) {
+        wrapper.apply(savedThis, savedArgs);
+        savedArgs = savedThis = null;
+      }
+    }, ms);
+  }
+
+  return wrapper;
+}
+
 // parse error to get the readable string in Chrome and Firefox
 function parseError(error) {
-  const isFirefox = navigator.userAgent.toLowerCase().indexOf('firefox') > -1;
+  const isFirefox = navigator.userAgent.toLowerCase().indexOf("firefox") > -1;
   const errorString = isFirefox ? error.toString() + " " + error.stack : error.stack;
-  const regex =/(\b(https?|ftp|file):\/\/[-A-Z0-9+&@#\/%?=~_|!:,.;]*[-A-Z0-9+&@#\/%=~_|])/ig;
-  const errorNoURL = errorString.replace(regex, url => '<i>' + last(url.split("/")) + '</i>');
-  const errorParsed = errorNoURL.replace(/at /ig, "<br>&nbsp;&nbsp;at ");
+  const regex = /(\b(https?|ftp|file):\/\/[-A-Z0-9+&@#\/%?=~_|!:,.;]*[-A-Z0-9+&@#\/%=~_|])/gi;
+  const errorNoURL = errorString.replace(regex, url => "<i>" + last(url.split("/")) + "</i>");
+  const errorParsed = errorNoURL.replace(/at /gi, "<br>&nbsp;&nbsp;at ");
   return errorParsed;
 }
 
 // polyfills
 if (Array.prototype.flat === undefined) {
-  Array.prototype.flat = function() {
-    return this.reduce((acc, val) => Array.isArray(val) ? acc.concat(val.flat()) : acc.concat(val), []);
-  }
+  Array.prototype.flat = function () {
+    return this.reduce((acc, val) => (Array.isArray(val) ? acc.concat(val.flat()) : acc.concat(val)), []);
+  };
 }
 
 // check if string is a valid for JSON parse
 JSON.isValid = str => {
-  try {JSON.parse(str);}
-  catch(e) {return false;}
+  try {
+    JSON.parse(str);
+  } catch (e) {
+    return false;
+  }
   return true;
-}
+};
 
 function getBase64(url, callback) {
   const xhr = new XMLHttpRequest();
@@ -640,16 +709,16 @@ function wiki(page) {
 
 // wrap URL into html a element
 function link(URL, description) {
-  return `<a href="${URL}" rel="noopener" target="_blank">${description}</a>`
+  return `<a href="${URL}" rel="noopener" target="_blank">${description}</a>`;
 }
 
 function isCtrlClick(event) {
   // meta key is cmd key on MacOs
-  return event.ctrlKey || event.metaKey;
+  return event.ctrlKey || event.metaKey;
 }
 
 function generateDate(from = 100, to = 1000) {
-  return new Date(rand(from, to),rand(12),rand(31)).toLocaleDateString("en", {year:'numeric', month:'long', day:'numeric'});
+  return new Date(rand(from, to), rand(12), rand(31)).toLocaleDateString("en", {year: "numeric", month: "long", day: "numeric"});
 }
 
 function getQGIScoordinates(x, y) {
@@ -659,15 +728,18 @@ function getQGIScoordinates(x, y) {
 }
 
 // prompt replacer (prompt does not work in Electron)
-void function() {
+void (function () {
   const prompt = document.getElementById("prompt");
   const form = prompt.querySelector("#promptForm");
 
-  window.prompt = function(promptText = "Please provide an input", options = {default:1, step:.01, min:0, max:100}, callback) {
-    if (options.default === undefined) {ERROR && console.error("Prompt: options object does not have default value defined"); return;}
+  window.prompt = function (promptText = "Please provide an input", options = {default: 1, step: 0.01, min: 0, max: 100}, callback) {
+    if (options.default === undefined) {
+      ERROR && console.error("Prompt: options object does not have default value defined");
+      return;
+    }
     const input = prompt.querySelector("#promptInput");
     prompt.querySelector("#promptText").innerHTML = promptText;
-    const type = typeof(options.default) === "number" ? "number" : "text";
+    const type = typeof options.default === "number" ? "number" : "text";
     input.type = type;
     if (options.step !== undefined) input.step = options.step;
     if (options.min !== undefined) input.min = options.min;
@@ -676,17 +748,56 @@ void function() {
     input.value = options.default;
     prompt.style.display = "block";
 
-    form.addEventListener("submit", event => {
-      prompt.style.display = "none";
-      const v = type === "number" ? +input.value : input.value;
-      event.preventDefault();
-      if (callback) callback(v);
-    }, {once: true});
-  }
+    form.addEventListener(
+      "submit",
+      event => {
+        prompt.style.display = "none";
+        const v = type === "number" ? +input.value : input.value;
+        event.preventDefault();
+        if (callback) callback(v);
+      },
+      {once: true}
+    );
+  };
 
   const cancel = prompt.querySelector("#promptCancel");
-  cancel.addEventListener("click", () => prompt.style.display = "none");
-}()
+  cancel.addEventListener("click", () => (prompt.style.display = "none"));
+})();
 
 // indexedDB; ldb object
-!function(){function e(t,o){return n?void(n.transaction("s").objectStore("s").get(t).onsuccess=function(e){var t=e.target.result&&e.target.result.v||null;o(t)}):void setTimeout(function(){e(t,o)},100)}var t=window.indexedDB||window.mozIndexedDB||window.webkitIndexedDB||window.msIndexedDB;if(!t)return void ERROR && console.error("indexedDB not supported");var n,o={k:"",v:""},r=t.open("d2",1);r.onsuccess=function(e){n=this.result},r.onerror=function(e){ERROR && console.error("indexedDB request error"),INFO && console.log(e)},r.onupgradeneeded=function(e){n=null;var t=e.target.result.createObjectStore("s",{keyPath:"k"});t.transaction.oncomplete=function(e){n=e.target.db}},window.ldb={get:e,set:function(e,t){o.k=e,o.v=t,n.transaction("s","readwrite").objectStore("s").put(o)}}}();
\ No newline at end of file
+!(function () {
+  function e(t, o) {
+    return n
+      ? void (n.transaction("s").objectStore("s").get(t).onsuccess = function (e) {
+          var t = (e.target.result && e.target.result.v) || null;
+          o(t);
+        })
+      : void setTimeout(function () {
+          e(t, o);
+        }, 100);
+  }
+  var t = window.indexedDB || window.mozIndexedDB || window.webkitIndexedDB || window.msIndexedDB;
+  if (!t) return void ERROR && console.error("indexedDB not supported");
+  var n,
+    o = {k: "", v: ""},
+    r = t.open("d2", 1);
+  (r.onsuccess = function (e) {
+    n = this.result;
+  }),
+    (r.onerror = function (e) {
+      ERROR && console.error("indexedDB request error"), INFO && console.log(e);
+    }),
+    (r.onupgradeneeded = function (e) {
+      n = null;
+      var t = e.target.result.createObjectStore("s", {keyPath: "k"});
+      t.transaction.oncomplete = function (e) {
+        n = e.target.db;
+      };
+    }),
+    (window.ldb = {
+      get: e,
+      set: function (e, t) {
+        (o.k = e), (o.v = t), n.transaction("s", "readwrite").objectStore("s").put(o);
+      }
+    });
+})();