LibJS: Add Array.prototype.forEach()

Author: https://github.com/linusg
Commit: 866172a721
Pull-request: https://github.com/SerenityOS/serenity/pull/1793

Libraries/LibJS/Runtime/ArrayPrototype.cpp

@@ -1,5 +1,6 @@
 /*
  * Copyright (c) 2020, Andreas Kling <kling@serenityos.org>
+ * Copyright (c) 2020, Linus Groh <mail@linusgroh.de>
  * All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
@@ -31,12 +32,14 @@
 #include <LibJS/Runtime/Array.h>
 #include <LibJS/Runtime/ArrayPrototype.h>
 #include <LibJS/Runtime/Error.h>
+#include <LibJS/Runtime/Function.h>
 #include <LibJS/Runtime/Value.h>
 
 namespace JS {
 
 ArrayPrototype::ArrayPrototype()
 {
+    put_native_function("forEach", for_each, 1);
     put_native_function("pop", pop, 0);
     put_native_function("push", push, 1);
     put_native_function("shift", shift, 0);
@@ -61,6 +64,43 @@ static Array* array_from(Interpreter& interpreter)
     return static_cast<Array*>(this_object);
 }
 
+static Function* callback_from_args(Interpreter& interpreter, const String& name)
+{
+    if (interpreter.argument_count() < 1) {
+        interpreter.throw_exception<TypeError>(String::format("Array.prototype.%s() requires at least one argument", name.characters()));
+        return nullptr;
+    }
+    auto callback = interpreter.argument(0);
+    if (!callback.is_object() || !callback.as_object().is_function()) {
+        interpreter.throw_exception<TypeError>(String::format("%s is not a function", callback.to_string().characters()));
+        return nullptr;
+    }
+    return static_cast<Function*>(&callback.as_object());
+}
+
+Value ArrayPrototype::for_each(Interpreter& interpreter)
+{
+    auto* array = array_from(interpreter);
+    if (!array)
+        return {};
+    auto* callback = callback_from_args(interpreter, "forEach");
+    if (!callback)
+        return {};
+    auto this_value = interpreter.argument(1);
+    auto initial_array_size = array->elements().size();
+    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;
+        interpreter.call(callback, this_value, { value, Value((i32)i), array });
+        if (interpreter.exception())
+            return {};
+    }
+    return js_undefined();
+}
+
 Value ArrayPrototype::push(Interpreter& interpreter)
 {
     auto* array = array_from(interpreter);

Libraries/LibJS/Runtime/ArrayPrototype.h

@@ -1,5 +1,6 @@
 /*
  * Copyright (c) 2020, Andreas Kling <kling@serenityos.org>
+ * Copyright (c) 2020, Linus Groh <mail@linusgroh.de>
  * All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
@@ -38,6 +39,7 @@ public:
 private:
     virtual const char* class_name() const override { return "ArrayPrototype"; }
 
+    static Value for_each(Interpreter&);
     static Value pop(Interpreter&);
     static Value push(Interpreter&);
     static Value shift(Interpreter&);

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

@@ -0,0 +1,64 @@
+load("test-common.js");
+
+try {
+    assert(Array.prototype.forEach.length === 1);
+
+    try {
+        [].forEach();
+        assertNotReached();
+    } catch (e) {
+        assert(e.name === "TypeError");
+        assert(e.message === "Array.prototype.forEach() requires at least one argument");
+    }
+
+    try {
+        [].forEach(undefined);
+        assertNotReached();
+    } catch (e) {
+        assert(e.name === "TypeError");
+        assert(e.message === "undefined is not a function");
+    }
+
+    var a = [1, 2, 3];
+    var o = {};
+    var callbackCalled = 0;
+    var callback = () => { callbackCalled++; };
+
+    assert([].forEach(callback) === undefined);
+    assert(callbackCalled === 0);
+
+    assert(a.forEach(callback) === undefined);
+    assert(callbackCalled === 3);
+
+    callbackCalled = 0;
+    a.forEach(function(value, index) {
+        assert(value === a[index]);
+        assert(index === a[index] - 1);
+    });
+
+    callbackCalled = 0;
+    a.forEach(function(_, _, array) {
+        callbackCalled++;
+        assert(a.length === array.length);
+        a.push("test");
+    });
+    assert(callbackCalled === 3);
+    assert(a.length === 6);
+
+    callbackCalled = 0;
+    a.forEach(function(value, index) {
+        callbackCalled++;
+        this[index] = value;
+    }, o);
+    assert(callbackCalled === 6);
+    assert(o[0] === 1);
+    assert(o[1] === 2);
+    assert(o[2] === 3);
+    assert(o[3] === "test");
+    assert(o[4] === "test");
+    assert(o[5] === "test");
+
+    console.log("PASS");
+} catch (e) {
+    console.log("FAIL: " + e);
+}