feat: 计算文字宽度

✅ Closes: #15

src/index.ts

@@ -13,3 +13,4 @@ export * from "./lib/CoordinateUtils";
 export * from "./lib/ajax";
 export * from "./lib/browser";
 export * from "./lib/getJson";
+export * from "./lib/computedTextWidth";

src/lib/computedTextWidth.ts

@@ -0,0 +1,15 @@
+let canvas: HTMLCanvasElement;
+
+/**
+ * 计算文本宽度
+ * @param {string} text - 文本
+ * @param {string} font - 字体
+ * @returns {number} - 宽度
+ */
+export function computedTextWidth(text: string, font: string) {
+  canvas = canvas ?? document.createElement("canvas");
+  const context = canvas.getContext("2d");
+  context!.font = font;
+  const metrics = context!.measureText(text);
+  return metrics.width;
+}