LibJS: Add %TypedArray%.prototype.lastIndexOf

Userland/Libraries/LibJS/Runtime/TypedArrayPrototype.cpp

@@ -36,6 +36,7 @@ void TypedArrayPrototype::initialize(GlobalObject& object)
     define_native_function(vm.names.forEach, for_each, 1, attr);
     define_native_function(vm.names.includes, includes, 1, attr);
     define_native_function(vm.names.indexOf, index_of, 1, attr);
+    define_native_function(vm.names.lastIndexOf, last_index_of, 1, attr);
     define_native_function(vm.names.some, some, 1, attr);
     define_native_function(vm.names.join, join, 1, attr);
     define_native_function(vm.names.keys, keys, 0, attr);
@@ -355,6 +356,54 @@ JS_DEFINE_NATIVE_FUNCTION(TypedArrayPrototype::index_of)
     return Value(-1);
 }
 
+// 23.2.3.17 %TypedArray%.prototype.lastIndexOf ( searchElement [ , fromIndex ] ), https://tc39.es/ecma262/#sec-%typedarray%.prototype.lastindexof
+JS_DEFINE_NATIVE_FUNCTION(TypedArrayPrototype::last_index_of)
+{
+    auto typed_array = typed_array_from(vm, global_object);
+    if (!typed_array)
+        return {};
+
+    auto length = typed_array->array_length();
+
+    if (length == 0)
+        return Value(-1);
+
+    double n;
+    if (vm.argument_count() > 1) {
+        n = vm.argument(1).to_integer_or_infinity(global_object);
+        if (vm.exception())
+            return {};
+    } else {
+        n = length - 1;
+    }
+
+    if (Value(n).is_negative_infinity())
+        return Value(-1);
+
+    i32 k;
+    if (n >= 0) {
+        k = min(n, (i32)length - 1);
+    } else {
+        auto relative_k = length + n;
+        if (relative_k < 0) // ensures we dont underflow `k`
+            relative_k = -1;
+        k = relative_k;
+    }
+
+    auto search_element = vm.argument(0);
+    for (; k >= 0; --k) {
+        auto k_present = typed_array->has_property(k);
+        if (k_present) {
+            auto element_k = typed_array->get(k);
+
+            if (strict_eq(search_element, element_k))
+                return Value(k);
+        }
+    }
+
+    return Value(-1);
+}
+
 // 23.2.3.25 %TypedArray%.prototype.some ( callbackfn [ , thisArg ] ), https://tc39.es/ecma262/#sec-%typedarray%.prototype.some
 JS_DEFINE_NATIVE_FUNCTION(TypedArrayPrototype::some)
 {

Userland/Libraries/LibJS/Runtime/TypedArrayPrototype.h

@@ -33,6 +33,7 @@ private:
     JS_DECLARE_NATIVE_FUNCTION(for_each);
     JS_DECLARE_NATIVE_FUNCTION(includes);
     JS_DECLARE_NATIVE_FUNCTION(index_of);
+    JS_DECLARE_NATIVE_FUNCTION(last_index_of);
     JS_DECLARE_NATIVE_FUNCTION(some);
     JS_DECLARE_NATIVE_FUNCTION(join);
     JS_DECLARE_NATIVE_FUNCTION(keys);

Userland/Libraries/LibJS/Tests/builtins/TypedArray/TypedArray.prototype.lastIndexOf.js

@@ -0,0 +1,44 @@
+const TYPED_ARRAYS = [
+    Uint8Array,
+    Uint8ClampedArray,
+    Uint16Array,
+    Uint32Array,
+    Int8Array,
+    Int16Array,
+    Int32Array,
+    Float32Array,
+    Float64Array,
+];
+
+const BIGINT_TYPED_ARRAYS = [BigUint64Array, BigInt64Array];
+
+test("basic functionality", () => {
+    TYPED_ARRAYS.forEach(T => {
+        expect(T.prototype.lastIndexOf).toHaveLength(1);
+
+        const typedArray = new T(3);
+        typedArray[0] = 1;
+        typedArray[1] = 2;
+        typedArray[2] = 2;
+
+        expect(typedArray.lastIndexOf(2)).toBe(2);
+        expect(typedArray.lastIndexOf(-1)).toBe(-1);
+        expect(typedArray.lastIndexOf(Infinity)).toBe(-1);
+        expect(typedArray.lastIndexOf(2, 2)).toBe(2);
+        expect(typedArray.lastIndexOf(2, -2)).toBe(1);
+    });
+
+    BIGINT_TYPED_ARRAYS.forEach(T => {
+        expect(T.prototype.lastIndexOf).toHaveLength(1);
+
+        const typedArray = new T(3);
+        typedArray[0] = 1n;
+        typedArray[1] = 2n;
+        typedArray[2] = 2n;
+
+        expect(typedArray.lastIndexOf(2n)).toBe(2);
+        expect(typedArray.lastIndexOf(-1n)).toBe(-1);
+        expect(typedArray.lastIndexOf(2n, 2)).toBe(2);
+        expect(typedArray.lastIndexOf(2n, -2)).toBe(1);
+    });
+});