LibJS: Add Array.prototype.map()

Author: https://github.com/linusg
Commit: f7df521073
Pull-request: https://github.com/SerenityOS/serenity/pull/1793

Libraries/LibJS/Runtime/ArrayPrototype.cpp

@@ -41,6 +41,7 @@ ArrayPrototype::ArrayPrototype()
 {
     put_native_function("filter", filter, 1);
     put_native_function("forEach", for_each, 1);
+    put_native_function("map", map, 1);
     put_native_function("pop", pop, 0);
     put_native_function("push", push, 1);
     put_native_function("shift", shift, 0);
@@ -128,6 +129,31 @@ Value ArrayPrototype::for_each(Interpreter& interpreter)
     return js_undefined();
 }
 
+Value ArrayPrototype::map(Interpreter& interpreter)
+{
+    auto* array = array_from(interpreter);
+    if (!array)
+        return {};
+    auto* callback = callback_from_args(interpreter, "map");
+    if (!callback)
+        return {};
+    auto this_value = interpreter.argument(1);
+    auto initial_array_size = array->elements().size();
+    auto* new_array = interpreter.heap().allocate<Array>();
+    for (size_t i = 0; i < initial_array_size; ++i) {
+        if (i >= array->elements().size())
+            break;
+        auto value = array->elements()[i];
+        if (value.is_empty())
+            continue;
+        auto result = interpreter.call(callback, this_value, { value, Value((i32)i), array });
+        if (interpreter.exception())
+            return {};
+        new_array->elements().append(result);
+    }
+    return Value(new_array);
+}
+
 Value ArrayPrototype::push(Interpreter& interpreter)
 {
     auto* array = array_from(interpreter);

Libraries/LibJS/Runtime/ArrayPrototype.h

@@ -41,6 +41,7 @@ private:
 
     static Value filter(Interpreter&);
     static Value for_each(Interpreter&);
+    static Value map(Interpreter&);
     static Value pop(Interpreter&);
     static Value push(Interpreter&);
     static Value shift(Interpreter&);

Libraries/LibJS/Tests/Array.prototype.map.js

@@ -0,0 +1,51 @@
+load("test-common.js");
+
+try {
+    assert(Array.prototype.map.length === 1);
+
+    try {
+        [].map();
+        assertNotReached();
+    } catch (e) {
+        assert(e.name === "TypeError");
+        assert(e.message === "Array.prototype.map() requires at least one argument");
+    }
+
+    try {
+        [].map(undefined);
+        assertNotReached();
+    } catch (e) {
+        assert(e.name === "TypeError");
+        assert(e.message === "undefined is not a function");
+    }
+
+    var callbackCalled = 0;
+    var callback = () => { callbackCalled++; };
+
+    assert([].map(callback).length === 0);
+    assert(callbackCalled === 0);
+
+    assert([1, 2, 3].map(callback).length === 3);
+    assert(callbackCalled === 3);
+
+    var results = [undefined, null, true, "foo", 42, {}].map((value, index) => "" + index + " -> " + value);
+    assert(results.length === 6);
+    assert(results[0] === "0 -> undefined");
+    assert(results[1] === "1 -> null");
+    assert(results[2] === "2 -> true");
+    assert(results[3] === "3 -> foo");
+    assert(results[4] === "4 -> 42");
+    assert(results[5] === "5 -> [object Object]");
+
+    var squaredNumbers = [0, 1, 2, 3, 4].map(x => x ** 2);
+    assert(squaredNumbers.length === 5);
+    assert(squaredNumbers[0] === 0);
+    assert(squaredNumbers[1] === 1);
+    assert(squaredNumbers[2] === 4);
+    assert(squaredNumbers[3] === 9);
+    assert(squaredNumbers[4] === 16);
+
+    console.log("PASS");
+} catch (e) {
+    console.log("FAIL: " + e);
+}