LibJS: Add spec comments and check for edge cases in Math.asinh

Userland/Libraries/LibJS/Runtime/MathObject.cpp

@@ -337,7 +337,15 @@ JS_DEFINE_NATIVE_FUNCTION(MathObject::asin)
 // 21.3.2.5 Math.asinh ( x ), https://tc39.es/ecma262/#sec-math.asinh
 JS_DEFINE_NATIVE_FUNCTION(MathObject::asinh)
 {
-    return Value(::asinh(TRY(vm.argument(0).to_number(vm)).as_double()));
+    // 1. Let n be ? ToNumber(x).
+    auto number = TRY(vm.argument(0).to_number(vm));
+
+    // 2. If n is not finite or n is either +0𝔽 or -0𝔽, return n.
+    if (!number.is_finite_number() || number.is_positive_zero() || number.is_negative_zero())
+        return number;
+
+    // 3. Return an implementation-approximated Number value representing the result of the inverse hyperbolic sine of ℝ(n).
+    return Value(::asinh(number.as_double()));
 }
 
 // 21.3.2.6 Math.atan ( x ), https://tc39.es/ecma262/#sec-math.atan

Userland/Libraries/LibJS/Tests/builtins/Math/Math.asinh.js

@@ -3,4 +3,9 @@ test("basic functionality", () => {
 
     expect(Math.asinh(0)).toBeCloseTo(0);
     expect(Math.asinh(1)).toBeCloseTo(0.881373);
+    expect(Math.asinh(NaN)).toBe(NaN);
+    expect(Math.asinh(Number.POSITIVE_INFINITY)).toBe(Number.POSITIVE_INFINITY);
+    expect(Math.asinh(Number.NEGATIVE_INFINITY)).toBe(Number.NEGATIVE_INFINITY);
+    expect(Math.asinh(0.0)).toBe(0.0);
+    expect(Math.asinh(-0.0)).toBe(-0.0);
 });