diff --git a/src/utils/commonUtils.test.ts b/src/utils/commonUtils.test.ts
new file mode 100644
index 00000000..6ca595d3
--- /dev/null
+++ b/src/utils/commonUtils.test.ts
@@ -0,0 +1,97 @@
+import { expect, describe, it } from 'vitest'
+import { getLongitude, getLatitude, getCoordinates } from './commonUtils'
+
+describe('getLongitude', () => {
+  const mapCoordinates = { lonW: -10, lonT: 20 };
+  const graphWidth = 1000;
+
+  it('should calculate longitude at the left edge (x=0)', () => {
+    expect(getLongitude(0, mapCoordinates, graphWidth, 2)).toBe(-10);
+  });
+
+  it('should calculate longitude at the right edge (x=graphWidth)', () => {
+    expect(getLongitude(1000, mapCoordinates, graphWidth, 2)).toBe(10);
+  });
+
+  it('should calculate longitude at the center (x=graphWidth/2)', () => {
+    expect(getLongitude(500, mapCoordinates, graphWidth, 2)).toBe(0);
+  });
+
+  it('should respect decimal precision', () => {
+    // 333/1000 * 20 = 6.66, -10 + 6.66 = -3.34
+    expect(getLongitude(333, mapCoordinates, graphWidth, 4)).toBe(-3.34);
+  });
+
+  it('should handle different map coordinate ranges', () => {
+    const wideMap = { lonW: -180, lonT: 360 };
+    expect(getLongitude(500, wideMap, graphWidth, 2)).toBe(0);
+    expect(getLongitude(0, wideMap, graphWidth, 2)).toBe(-180);
+    expect(getLongitude(1000, wideMap, graphWidth, 2)).toBe(180);
+  });
+});
+
+describe('getLatitude', () => {
+  const mapCoordinates = { latN: 60, latT: 40 };
+  const graphHeight = 800;
+
+  it('should calculate latitude at the top edge (y=0)', () => {
+    expect(getLatitude(0, mapCoordinates, graphHeight, 2)).toBe(60);
+  });
+
+  it('should calculate latitude at the bottom edge (y=graphHeight)', () => {
+    expect(getLatitude(800, mapCoordinates, graphHeight, 2)).toBe(20);
+  });
+
+  it('should calculate latitude at the center (y=graphHeight/2)', () => {
+    expect(getLatitude(400, mapCoordinates, graphHeight, 2)).toBe(40);
+  });
+
+  it('should respect decimal precision', () => {
+    // 60 - (333/800 * 40) = 60 - 16.65 = 43.35
+    expect(getLatitude(333, mapCoordinates, graphHeight, 4)).toBe(43.35);
+  });
+
+  it('should handle equator-centered maps', () => {
+    const equatorMap = { latN: 45, latT: 90 };
+    expect(getLatitude(400, equatorMap, graphHeight, 2)).toBe(0);
+  });
+});
+
+describe('getCoordinates', () => {
+  const mapCoordinates = { lonW: -10, lonT: 20, latN: 60, latT: 40 };
+  const graphWidth = 1000;
+  const graphHeight = 800;
+
+  it('should return [longitude, latitude] tuple', () => {
+    const result = getCoordinates(500, 400, mapCoordinates, graphWidth, graphHeight, 2);
+    expect(result).toEqual([0, 40]);
+  });
+
+  it('should calculate coordinates at top-left corner', () => {
+    const result = getCoordinates(0, 0, mapCoordinates, graphWidth, graphHeight, 2);
+    expect(result).toEqual([-10, 60]);
+  });
+
+  it('should calculate coordinates at bottom-right corner', () => {
+    const result = getCoordinates(1000, 800, mapCoordinates, graphWidth, graphHeight, 2);
+    expect(result).toEqual([10, 20]);
+  });
+
+  it('should respect decimal precision for both coordinates', () => {
+    const result = getCoordinates(333, 333, mapCoordinates, graphWidth, graphHeight, 4);
+    expect(result[0]).toBe(-3.34); // longitude
+    expect(result[1]).toBe(43.35); // latitude
+  });
+
+  it('should use default precision of 2 decimals', () => {
+    const result = getCoordinates(333, 333, mapCoordinates, graphWidth, graphHeight);
+    expect(result[0]).toBe(-3.34);
+    expect(result[1]).toBe(43.35);
+  });
+
+  it('should handle global map coordinates', () => {
+    const globalMap = { lonW: -180, lonT: 360, latN: 90, latT: 180 };
+    const result = getCoordinates(500, 400, globalMap, graphWidth, graphHeight, 2);
+    expect(result).toEqual([0, 0]); // center of the world
+  });
+});
diff --git a/src/utils/commonUtils.ts b/src/utils/commonUtils.ts
index d5f2fc9a..e15f65cb 100644
--- a/src/utils/commonUtils.ts
+++ b/src/utils/commonUtils.ts
@@ -317,4 +317,9 @@ declare global {
     getLatitude: typeof getLatitude;
     getCoordinates: typeof getCoordinates;
   }
+
+  // Global variables defined in main.js
+  var mapCoordinates: { latT?: number; latN?: number; latS?: number; lonT?: number; lonW?: number; lonE?: number };
+  var graphWidth: number;
+  var graphHeight: number;
 }
\ No newline at end of file
diff --git a/src/utils/index.ts b/src/utils/index.ts
index 73581a38..e75d88cb 100644
--- a/src/utils/index.ts
+++ b/src/utils/index.ts
@@ -116,7 +116,7 @@ window.isLand = (i: number) => isLand(i, (window as any).pack);
 window.isWater = (i: number) => isWater(i, (window as any).pack);
 
 import { clipPoly, getSegmentId, debounce, throttle, parseError, getBase64, openURL, wiki, link, isCtrlClick, generateDate, getLongitude, getLatitude, getCoordinates, initializePrompt } from "./commonUtils";
-window.clipPoly = (points: [number, number][], secure?: number) => clipPoly(points, (window as any).graphWidth, (window as any).graphHeight, secure);
+window.clipPoly = (points: [number, number][], secure?: number) => clipPoly(points, graphWidth, graphHeight, secure);
 window.getSegmentId = getSegmentId;
 window.debounce = debounce;
 window.throttle = throttle;
@@ -127,9 +127,9 @@ window.wiki = wiki;
 window.link = link;
 window.isCtrlClick = isCtrlClick;
 window.generateDate = generateDate;
-window.getLongitude = (x: number, decimals?: number) => getLongitude(x, (window as any).mapCoordinates, (window as any).graphWidth, decimals);
-window.getLatitude = (y: number, decimals?: number) => getLatitude(y, (window as any).mapCoordinates, (window as any).graphHeight, decimals);
-window.getCoordinates = (x: number, y: number, decimals?: number) => getCoordinates(x, y, (window as any).mapCoordinates, (window as any).graphWidth, (window as any).graphHeight, decimals);
+window.getLongitude = (x: number, decimals?: number) => getLongitude(x, mapCoordinates, graphWidth, decimals);
+window.getLatitude = (y: number, decimals?: number) => getLatitude(y, mapCoordinates, graphHeight, decimals);
+window.getCoordinates = (x: number, y: number, decimals?: number) => getCoordinates(x, y, mapCoordinates, graphWidth, graphHeight, decimals);
 
 // Initialize prompt when DOM is ready
 if (document.readyState === 'loading') {