LibJS: Add Math.expm1()

3 files changed, 31 insertions, 0 deletions

diff --git a/Libraries/LibJS/Runtime/MathObject.cpp b/Libraries/LibJS/Runtime/MathObject.cpp
index e4f6072a58..2b173bcc70 100644
--- a/Libraries/LibJS/Runtime/MathObject.cpp
+++ b/Libraries/LibJS/Runtime/MathObject.cpp
@@ -51,6 +51,7 @@ MathObject::MathObject()
     put_native_function("tan", tan, 1, attr);
     put_native_function("pow", pow, 2, attr);
     put_native_function("exp", exp, 1, attr);
+    put_native_function("expm1", expm1, 1, attr);
     put_native_function("sign", sign, 1, attr);
 
     put("E", Value(M_E), 0);
@@ -218,6 +219,16 @@ Value MathObject::exp(Interpreter& interpreter)
     return Value(::pow(M_E, number.as_double()));
 }
 
+Value MathObject::expm1(Interpreter& interpreter)
+{
+    auto number = interpreter.argument(0).to_number(interpreter);
+    if (interpreter.exception())
+        return {};
+    if (number.is_nan())
+        return js_nan();
+    return Value(::pow(M_E, number.as_double()) - 1);
+}
+
 Value MathObject::sign(Interpreter& interpreter)
 {
     auto number = interpreter.argument(0).to_number(interpreter);
diff --git a/Libraries/LibJS/Runtime/MathObject.h b/Libraries/LibJS/Runtime/MathObject.h
index 31d9b7fd03..e9902e6d53 100644
--- a/Libraries/LibJS/Runtime/MathObject.h
+++ b/Libraries/LibJS/Runtime/MathObject.h
@@ -52,6 +52,7 @@ private:
     static Value tan(Interpreter&);
     static Value pow(Interpreter&);
     static Value exp(Interpreter&);
+    static Value expm1(Interpreter&);
     static Value sign(Interpreter&);
 };
 
diff --git a/Libraries/LibJS/Tests/Math.expm1.js b/Libraries/LibJS/Tests/Math.expm1.js
new file mode 100644
index 0000000000..45f3c2be54
--- /dev/null
+++ b/Libraries/LibJS/Tests/Math.expm1.js
@@ -0,0 +1,19 @@
+load("test-common.js");
+
+try {
+    assert(Math.expm1.length === 1);
+
+    assert(Math.expm1(0) === 0);
+    assert(isClose(Math.expm1(-2), -0.864664));
+    assert(isClose(Math.expm1(-1), -0.632120));
+    assert(isClose(Math.expm1(1), 1.718281));
+    assert(isClose(Math.expm1(2), 6.389056));
+
+    assert(isNaN(Math.expm1()));
+    assert(isNaN(Math.expm1(undefined)));
+    assert(isNaN(Math.expm1("foo")));
+
+    console.log("PASS");
+} catch (e) {
+    console.log("FAIL: " + e);
+}