LibJS: Handle +Infinity, -Infinity, +0 and -0 in modulo operator

Fixes 11 test262 cases.

Author: Lubrsi

Userland/Libraries/LibJS/Runtime/Value.cpp

@@ -1212,11 +1212,36 @@ Value mod(GlobalObject& global_object, Value lhs, Value rhs)
     if (vm.exception())
         return {};
     if (both_number(lhs_numeric, rhs_numeric)) {
+        // 6.1.6.1.6 Number::remainder ( n, d ), https://tc39.es/ecma262/#sec-numeric-types-number-remainder
+
+        // 1. If n is NaN or d is NaN, return NaN.
         if (lhs_numeric.is_nan() || rhs_numeric.is_nan())
             return js_nan();
+
+        // 2. If n is +∞𝔽 or n is -∞𝔽, return NaN.
+        if (lhs_numeric.is_positive_infinity() || lhs_numeric.is_negative_infinity())
+            return js_nan();
+
+        // 3. If d is +∞𝔽 or d is -∞𝔽, return n.
+        if (rhs_numeric.is_positive_infinity() || rhs_numeric.is_negative_infinity())
+            return lhs_numeric;
+
+        // 4. If d is +0𝔽 or d is -0𝔽, return NaN.
+        if (rhs_numeric.is_positive_zero() || rhs_numeric.is_negative_zero())
+            return js_nan();
+
+        // 5. If n is +0𝔽 or n is -0𝔽, return n.
+        if (lhs_numeric.is_positive_zero() || lhs_numeric.is_negative_zero())
+            return lhs_numeric;
+
+        // 6. Assert: n and d are finite and non-zero.
+
         auto index = lhs_numeric.as_double();
         auto period = rhs_numeric.as_double();
         auto trunc = (double)(i32)(index / period);
+
+        // 7. Let r be ℝ(n) - (ℝ(d) × q) where q is an integer that is negative if and only if n and d have opposite sign, and whose magnitude is as large as possible without exceeding the magnitude of ℝ(n) / ℝ(d).
+        // 8. Return 𝔽(r).
         return Value(index - trunc * period);
     }
     if (both_bigint(lhs_numeric, rhs_numeric)) {

Userland/Libraries/LibJS/Tests/operators/modulo-basic.js

@@ -13,4 +13,26 @@ test("basic functionality", () => {
     expect(-4 % 2).toBe(-0);
     expect(5.5 % 2).toBe(1.5);
     expect(NaN % 2).toBeNaN();
+    expect(2 % NaN).toBeNaN();
+    expect(NaN % NaN).toBeNaN();
+    expect(Infinity % 1).toBeNaN();
+    expect(-Infinity % 1).toBeNaN();
+    expect(1 % Infinity).toBe(1);
+    expect(1 % -Infinity).toBe(1);
+    expect(1 % 0).toBeNaN();
+    expect(1 % -0).toBeNaN();
+    expect(0 % 5).toBe(0);
+    expect(-0 % 5).toBe(-0);
+
+    // test262 examples
+    expect(1 % null).toBeNaN();
+    expect(null % 1).toBe(0);
+    expect(true % null).toBeNaN();
+    expect(null % true).toBe(0);
+    expect("1" % null).toBeNaN();
+    expect(null % "1").toBe(0);
+    expect(null % undefined).toBeNaN();
+    expect(undefined % null).toBeNaN();
+    expect(undefined % undefined).toBeNaN();
+    expect(null % null).toBeNaN();
 });