3 files changed, 36 insertions, 0 deletions
diff --git a/Libraries/LibJS/Runtime/GlobalObject.cpp b/Libraries/LibJS/Runtime/GlobalObject.cpp
index 7a1f062675..a0f3066629 100644
--- a/Libraries/LibJS/Runtime/GlobalObject.cpp
+++ b/Libraries/LibJS/Runtime/GlobalObject.cpp
@@ -87,6 +87,7 @@ void GlobalObject::initialize()
 
     put_native_function("gc", gc);
     put_native_function("isNaN", is_nan, 1);
+    put_native_function("isFinite", is_finite, 1);
 
     // FIXME: These are read-only in ES5
     put("NaN", js_nan());
@@ -141,4 +142,10 @@ Value GlobalObject::is_nan(Interpreter& interpreter)
     return Value(value.is_nan());
 }
 
+Value GlobalObject::is_finite(Interpreter& interpreter)
+{
+    auto value = interpreter.argument(0).to_number();
+    return Value(!value.is_infinity() && !value.is_nan());
+}
+
 }
diff --git a/Libraries/LibJS/Runtime/GlobalObject.h b/Libraries/LibJS/Runtime/GlobalObject.h
index 52ca09a3a0..d28383fac9 100644
--- a/Libraries/LibJS/Runtime/GlobalObject.h
+++ b/Libraries/LibJS/Runtime/GlobalObject.h
@@ -53,6 +53,7 @@ private:
 
     static Value gc(Interpreter&);
     static Value is_nan(Interpreter&);
+    static Value is_finite(Interpreter&);
 
     template<typename ConstructorType>
     void add_constructor(const FlyString& property_name, ConstructorType*&, Object& prototype);
diff --git a/Libraries/LibJS/Tests/isFinite.js b/Libraries/LibJS/Tests/isFinite.js
new file mode 100644
index 0000000000..095cab4018
--- /dev/null
+++ b/Libraries/LibJS/Tests/isFinite.js
@@ -0,0 +1,28 @@
+load("test-common.js");
+
+try {
+    assert(isFinite.length === 1);
+
+    assert(isFinite(0) === true);
+    assert(isFinite(42) === true);
+    assert(isFinite("") === true);
+    assert(isFinite("0") === true);
+    assert(isFinite("42") === true);
+    assert(isFinite(true) === true);
+    assert(isFinite(false) === true);
+    assert(isFinite(null) === true);
+    assert(isFinite([]) === true);
+
+    assert(isFinite() === false);
+    assert(isFinite(NaN) === false);
+    assert(isFinite(undefined) === false);
+    assert(isFinite(Infinity) === false);
+    assert(isFinite(-Infinity) === false);
+    assert(isFinite("foo") === false);
+    assert(isFinite({}) === false);
+    assert(isFinite([1, 2, 3]) === false);
+
+    console.log("PASS");
+} catch (e) {
+    console.log("FAIL: " + e.message);
+}