LibJS: Make StringToNumber case sensitive when falling back to strtod

We use strtod to convert a string to number after checking whether the
string is [+-]Infinity, however strtod also checks for either 'inf' or
'infinity' in a case-insensitive.
There are still valid cases for strtod to return infinity like 10e100000
so we just check if the "number" contains 'i' or 'I' in which case
the strtod infinity is not valid.

2 files changed, 19 insertions, 0 deletions

diff --git a/Userland/Libraries/LibJS/Runtime/Value.cpp b/Userland/Libraries/LibJS/Runtime/Value.cpp
index 77fc975649..7c3f9445d5 100644
--- a/Userland/Libraries/LibJS/Runtime/Value.cpp
+++ b/Userland/Libraries/LibJS/Runtime/Value.cpp
@@ -500,6 +500,11 @@ ThrowCompletionOr<Value> Value::to_number(GlobalObject& global_object) const
         auto parsed_double = strtod(string.characters(), &endptr);
         if (*endptr)
             return js_nan();
+        // NOTE: Per the spec only exactly [+-]Infinity should result in infinity
+        //       but strtod gives infinity for any case-insensitive 'infinity' or 'inf' string.
+        if (isinf(parsed_double) && string.contains('i', AK::CaseSensitivity::CaseInsensitive))
+            return js_nan();
+
         return Value(parsed_double);
     }
     case SYMBOL_TAG:
diff --git a/Userland/Libraries/LibJS/Tests/builtins/Number/Number.js b/Userland/Libraries/LibJS/Tests/builtins/Number/Number.js
index 7ee0f557a9..7a237dd21b 100644
--- a/Userland/Libraries/LibJS/Tests/builtins/Number/Number.js
+++ b/Userland/Libraries/LibJS/Tests/builtins/Number/Number.js
@@ -17,11 +17,18 @@ test("constructor without new", () => {
     expect(Number("Infinity")).toBe(Infinity);
     expect(Number("+Infinity")).toBe(Infinity);
     expect(Number("-Infinity")).toBe(-Infinity);
+    expect(Number("infinity")).toBeNaN();
+    expect(Number("-infinity")).toBeNaN();
+    expect(Number("INFINITY")).toBeNaN();
+    expect(Number("-INFINITY")).toBeNaN();
+    expect(Number("inf")).toBeNaN();
     expect(Number(undefined)).toBeNaN();
     expect(Number({})).toBeNaN();
     expect(Number({ a: 1 })).toBeNaN();
     expect(Number([1, 2, 3])).toBeNaN();
     expect(Number("foo")).toBeNaN();
+    expect(Number("10e10000")).toBe(Infinity);
+    expect(Number("-10e10000")).toBe(-Infinity);
 });
 
 test("constructor with new", () => {
@@ -38,9 +45,16 @@ test("constructor with new", () => {
     expect(new Number("Infinity").valueOf()).toBe(Infinity);
     expect(new Number("+Infinity").valueOf()).toBe(Infinity);
     expect(new Number("-Infinity").valueOf()).toBe(-Infinity);
+    expect(new Number("infinity").valueOf()).toBeNaN();
+    expect(new Number("-infinity").valueOf()).toBeNaN();
+    expect(new Number("INFINITY").valueOf()).toBeNaN();
+    expect(new Number("-INFINITY").valueOf()).toBeNaN();
+    expect(new Number("inf").valueOf()).toBeNaN();
     expect(new Number(undefined).valueOf()).toBeNaN();
     expect(new Number({}).valueOf()).toBeNaN();
     expect(new Number({ a: 1 }).valueOf()).toBeNaN();
     expect(new Number([1, 2, 3]).valueOf()).toBeNaN();
     expect(new Number("foo").valueOf()).toBeNaN();
+    expect(new Number("10e10000").valueOf()).toBe(Infinity);
+    expect(new Number("-10e10000").valueOf()).toBe(-Infinity);
 });