Added a NES Palette manager/generator which can export to assembler string of the palette data. Main.js has a little test code.

app/js/NESPalette.js

+
+
+export class NESPalette { 
+  constructor(){
+    this.__BGColor = 63; // Index to the background color ALL palettes MUST share.
+    this.__palette = [
+      // Tile/Background Palettes
+      0,0,0,
+      0,0,0,
+      0,0,0,
+      0,0,0,
+      // Sprite Palettes
+      0,0,0,
+      0,0,0,
+      0,0,0,
+      0,0,0
+    ];
+  }
+
+  set_palette(idx, p=8){
+    if (typeof(p) != 'number')
+      throw new TypeError("First argument expected to be a number.");
+    if (!(idx instanceof Array))
+      throw new TypeError("Expected an array of color index values.");
+    if (p < 0 || p >= 8){ // Setting ALL palettes!
+      if (idx.length != 25)
+        throw new RangeError("Color array must contain 25 color values to fill all palettes.");
+      this.__BGColor = idx[0];
+      for (var i=0; i < 24; i++){
+        this.__palette[i] = idx[i+1]
+      }
+    } else { // Setting a specific palette.
+      if (idx.length != 3)
+        throw new RangeError("Color array must contain three color values.");
+      p *= 3;
+      for (var i=0; i < 4; i++){
+        if (typeof(idx[i]) === 'number'){
+          this.__palette[p+i] = idx[i];
+        }
+      }
+    }
+  }
+
+  get_palette_syscolor_index(p, idx){
+    if (typeof(p) != 'number' || typeof(idx) != 'number')
+      throw new TypeError("Palette and color index expected to be numbers.");
+    if (p < 0 || p >= 8){
+      throw new RangeError("Palette index is out of bounds.");
+    }
+    if (idx < 0 || idx >= 4){
+      throw new RangeError("Palette color index is out of bounds.");
+    }
+    return (idx === 0) ? this.__BGColor : this.__palette[(p*3)+(idx-1)];
+  }
+
+  get_palette_color(p, idx){
+    if (typeof(p) != 'number' || typeof(idx) != 'number')
+      throw new TypeError("Palette and color index expected to be numbers.");
+    if (p < 0 || p >= 8){
+      throw new RangeError("Palette index is out of bounds.");
+    }
+    if (idx < 0 || idx >= 4){
+      throw new RangeError("Palette color index is out of bounds.");
+    }
+    return NESPalette.SystemColor(this.get_palette_syscolor_index(p, idx));
+  }
+
+  to_asm(memname="PaletteData"){
+    var NumToHex=function(n){
+      var h = n.toString(16);
+      if (h.length %2)
+        h = '0' + h;
+      return '$' + h;
+    };
+    var BGHex = NumToHex(this.__BGColor);
+    var s = memname + ":\n\t.db ";
+
+    // Storing background palette data.
+    for (var i=0; i < 12; i++){
+      if (i % 3 == 0)
+        s += ((i == 0) ? "" : " ") + BGHex;
+      s += " " + NumToHex(this.__palette[i]);
+    }
+    s += "\t; Background palette data.\n\t.db ";
+
+    // Storing foreground palette data.
+    for (var i=12; i < 24; i++){
+      if (i % 3 == 0)
+        s += ((i == 12) ? "" : " ") + BGHex;
+      s += " " + NumToHex(this.__palette[i]);
+    }
+    s += "\t; Foreground palette data.";
+
+    return s;
+  }
+}
+
+
+// NES Palette color information comes from the following site...
+// http://www.thealmightyguru.com/Games/Hacking/Wiki/index.php/NES_Palette 
+NESPalette.SystemColor = [
+  "#7C7C7C",
+  "#0000FC",
+  "#0000BC",
+  "#4428BC",
+  "#940084",
+  "#A80020",
+  "#A81000",
+  "#881400",
+  "#503000",
+  "#007800",
+  "#006800",
+  "#005800",
+  "#004058",
+  "#000000",
+  "#000000",
+  "#000000",
+  "#BCBCBC",
+  "#0078F8",
+  "#0058F8",
+  "#6844FC",
+  "#D800CC",
+  "#E40058",
+  "#F83800",
+  "#E45C10",
+  "#AC7C00",
+  "#00B800",
+  "#00A800",
+  "#00A844",
+  "#008888",
+  "#000000",
+  "#000000",
+  "#000000",
+  "#F8F8F8",
+  "#3CBCFC",
+  "#6888FC",
+  "#9878F8",
+  "#F878F8",
+  "#F85898",
+  "#F87858",
+  "#FCA044",
+  "#F8B800",
+  "#B8F818",
+  "#58D854",
+  "#58F898",
+  "#00E8D8",
+  "#787878",
+  "#000000",
+  "#000000",
+  "#FCFCFC",
+  "#A4E4FC",
+  "#B8B8F8",
+  "#D8B8F8",
+  "#F8B8F8",
+  "#F8A4C0",
+  "#F0D0B0",
+  "#FCE0A8",
+  "#F8D878",
+  "#D8F878",
+  "#B8F8B8",
+  "#B8F8D8",
+  "#00FCFC",
+  "#F8D8F8",
+  "#000000",
+  "#000000"
+];

app/js/main.js

+import {NESPalette} from "/app/js/NESPalette.js";
 
 
 function initialize(DOC){
   if (!ctx){
     throw new Error("Failed to obtain canvas context.");
   }
+
+  var nespal = new NESPalette();
+  nespal.set_palette([
+    44,
+    11,12,13,
+    54,23,43,
+    23,18,11,
+    4,8,60,
+    63,0,11,
+    0,15,14,
+    9,0,32,
+    5,10,20
+  ]);
+  console.log(nespal.to_asm());
 }
 
 

index.html

     <canvas id="painter" width:"128" height:"256"></canvas>
 
   </body>
-  <script src="app/js/main.js"></script>
+  <script src="app/js/main.js" type="module"></script>
 </html>