LibJS: Add the String.fromCodePoint() method

Userland/Libraries/LibJS/Runtime/CommonPropertyNames.h

@@ -128,6 +128,7 @@ namespace JS {
     P(freeze)                                \
     P(from)                                  \
     P(fromCharCode)                          \
+    P(fromCodePoint)                         \
     P(fromEntries)                           \
     P(fround)                                \
     P(gc)                                    \

Userland/Libraries/LibJS/Runtime/ErrorTypes.h

@@ -31,6 +31,7 @@
     M(InOperatorWithObject, "'in' operator must be used on an object")                                                                  \
     M(InstanceOfOperatorBadPrototype, "'prototype' property of {} is not an object")                                                    \
     M(InvalidAssignToConst, "Invalid assignment to const variable")                                                                     \
+    M(InvalidCodePoint, "Invalid code point {}, must be an integer no less than 0 and no greater than 0x10FFFF")                        \
     M(InvalidHint, "Invalid hint: \"{}\"")                                                                                              \
     M(InvalidIndex, "Index must be a positive integer")                                                                                 \
     M(InvalidLeftHandAssignment, "Invalid left-hand side in assignment")                                                                \

Userland/Libraries/LibJS/Runtime/StringConstructor.cpp

@@ -32,6 +32,7 @@ void StringConstructor::initialize(GlobalObject& global_object)
     u8 attr = Attribute::Writable | Attribute::Configurable;
     define_native_function(vm.names.raw, raw, 1, attr);
     define_native_function(vm.names.fromCharCode, from_char_code, 1, attr);
+    define_native_function(vm.names.fromCodePoint, from_code_point, 1, attr);
 }
 
 StringConstructor::~StringConstructor()
@@ -120,4 +121,26 @@ JS_DEFINE_NATIVE_FUNCTION(StringConstructor::from_char_code)
     return js_string(vm, builder.build());
 }
 
+// 22.1.2.2 String.fromCodePoint ( ...codePoints ), https://tc39.es/ecma262/#sec-string.fromcodepoint
+JS_DEFINE_NATIVE_FUNCTION(StringConstructor::from_code_point)
+{
+    StringBuilder builder;
+    for (size_t i = 0; i < vm.argument_count(); ++i) {
+        auto next_code_point = vm.argument(i).to_number(global_object);
+        if (vm.exception())
+            return {};
+        if (!next_code_point.is_integer()) {
+            vm.throw_exception<RangeError>(global_object, ErrorType::InvalidCodePoint, next_code_point.to_string_without_side_effects());
+            return {};
+        }
+        auto code_point = next_code_point.to_i32(global_object);
+        if (code_point < 0 || code_point > 0x10FFFF) {
+            vm.throw_exception<RangeError>(global_object, ErrorType::InvalidCodePoint, next_code_point.to_string_without_side_effects());
+            return {};
+        }
+        builder.append_code_point(code_point);
+    }
+    return js_string(vm, builder.build());
+}
+
 }

Userland/Libraries/LibJS/Runtime/StringConstructor.h

@@ -26,6 +26,7 @@ private:
 
     JS_DECLARE_NATIVE_FUNCTION(raw);
     JS_DECLARE_NATIVE_FUNCTION(from_char_code);
+    JS_DECLARE_NATIVE_FUNCTION(from_code_point);
 };
 
 }

Userland/Libraries/LibJS/Tests/builtins/String/String.fromCodePoint.js

@@ -0,0 +1,37 @@
+test("basic functionality", () => {
+    expect(String.fromCodePoint).toHaveLength(1);
+
+    expect(String.fromCodePoint()).toBe("");
+    expect(String.fromCodePoint(0)).toBe("\u0000");
+    expect(String.fromCodePoint(false)).toBe("\u0000");
+    expect(String.fromCodePoint(null)).toBe("\u0000");
+    expect(String.fromCodePoint(1)).toBe("\u0001");
+    expect(String.fromCodePoint(true)).toBe("\u0001");
+    expect(String.fromCodePoint(0xffff)).toBe("\uffff");
+    expect(String.fromCodePoint(65)).toBe("A");
+    expect(String.fromCodePoint(65, 66, 67)).toBe("ABC");
+    expect(String.fromCodePoint(228, 246, 252)).toBe("äöü");
+});
+
+test("errors", () => {
+    expect(() => {
+        String.fromCodePoint(NaN);
+    }).toThrowWithMessage(
+        RangeError,
+        "must be an integer no less than 0 and no greater than 0x10FFFF"
+    );
+
+    expect(() => {
+        String.fromCodePoint(-5);
+    }).toThrowWithMessage(
+        RangeError,
+        "must be an integer no less than 0 and no greater than 0x10FFFF"
+    );
+
+    expect(() => {
+        String.fromCodePoint(0x123ffff);
+    }).toThrowWithMessage(
+        RangeError,
+        "must be an integer no less than 0 and no greater than 0x10FFFF"
+    );
+});