Ignore misplaced negative signs in number formatter

src/number.ts

@@ -45,7 +45,7 @@ export const createNumberFormatter = (options: NumberFormatterOptions = {}): Num
     const decimalIndex = acceptsFraction ? value.indexOf(decimalSeparator) : -1;
     const integerSource = decimalIndex < 0 ? value : value.slice(0, decimalIndex);
     const fractionSource = decimalIndex < 0 ? "" : value.slice(decimalIndex + 1);
-    const negative = allowNegative && value.includes("-");
+    const negative = allowNegative && value.startsWith("-");
     let integer = integerSource.replace(/\D/g, "").replace(/^0+(?=\d)/, "");
     let fraction = fractionSource.replace(/\D/g, "");
 

tests/number-formatter.test.ts

@@ -24,14 +24,15 @@ describe("number formatter", () => {
   });
 
   test("supports signs, fixed precision, custom grouping, and disabled grouping", () => {
-    expect(
-      createNumberFormatter({
-        locales: "en-IN",
-        allowNegative: true,
-        minimumFractionDigits: 2,
-        maximumFractionDigits: 2,
-      }).format("-$12345678.9"),
-    ).toBe("-1,23,45,678.90");
+    const signed = createNumberFormatter({
+      locales: "en-IN",
+      allowNegative: true,
+      minimumFractionDigits: 2,
+      maximumFractionDigits: 2,
+    });
+
+    expect(signed.format("-$12345678.9")).toBe("-1,23,45,678.90");
+    expect(signed.format("1234-5678.9")).toBe("1,23,45,678.90");
 
     expect(
       createNumberFormatter({ useGrouping: false, maximumFractionDigits: 0 }).format("12,345"),

tests/rifm-format.browser.test.tsx

@@ -35,7 +35,7 @@ test("format works with real browser input", async () => {
   expect(await exec({ type: "PUT_SYMBOL", payload: "x" })).toBe("1|2’345");
 });
 
-test("keeps the caret after a negative sign", async () => {
+test("handles negative signs without moving or truncating digits", async () => {
   exec = createBrowserExec({
     ...createNumberFormatter({ allowNegative: true, maximumFractionDigits: 0 }),
   });
@@ -49,6 +49,15 @@ test("keeps the caret after a negative sign", async () => {
   });
 
   expect(await exec({ type: "PUT_SYMBOL", payload: "-" })).toBe("-|123");
+
+  exec.cleanup();
+  exec = createBrowserExec({
+    ...createNumberFormatter({ allowNegative: true, maximumFractionDigits: 0 }),
+    initialValue: "12345",
+  });
+
+  expect(await exec({ type: "MOVE_CARET", payload: 2 })).toBe("12|,345");
+  expect(await exec({ type: "PUT_SYMBOL", payload: "-" })).toBe("12|,345");
 });
 
 test("format with custom accept works with real browser input", async () => {