LibJS: Add Array.prototype.fill

Libraries/LibJS/Runtime/ArrayPrototype.cpp

@@ -68,6 +68,7 @@ ArrayPrototype::ArrayPrototype()
     put_native_function("some", some, 1, attr);
     put_native_function("every", every, 1, attr);
     put_native_function("splice", splice, 2, attr);
+    put_native_function("fill", fill, 1, attr);
     put("length", Value(0), Attribute::Configurable);
 }
 
@@ -743,4 +744,51 @@ Value ArrayPrototype::splice(Interpreter& interpreter)
     return removed_elements;
 }
 
+Value ArrayPrototype::fill(Interpreter& interpreter)
+{
+    auto *this_object = interpreter.this_value().to_object(interpreter);
+    if (!this_object)
+        return {};
+
+    ssize_t length = get_length(interpreter, *this_object);
+    if (interpreter.exception())
+        return {};
+
+    ssize_t relative_start = 0;
+    ssize_t relative_end = length;
+
+    if (interpreter.argument_count() >= 2) {
+        relative_start = interpreter.argument(1).to_i32(interpreter);
+        if (interpreter.exception())
+            return {};
+    }
+
+    if (interpreter.argument_count() >= 3) {
+        relative_end = interpreter.argument(2).to_i32(interpreter);
+        if (interpreter.exception())
+            return {};
+    }
+
+    size_t from, to;
+
+    if (relative_start < 0)
+        from = max(length + relative_start, 0L);
+    else
+        from = min(relative_start, length);
+
+    if (relative_end < 0)
+        to = max(length + relative_end, 0L);
+    else
+        to = min(relative_end, length);
+
+    for (size_t i = from; i < to; i++) {
+        this_object->put_by_index(i, interpreter.argument(0));
+        if (interpreter.exception())
+            return {};
+    }
+
+    return this_object;
 }
+
+}
+

Libraries/LibJS/Runtime/ArrayPrototype.h

@@ -61,6 +61,7 @@ private:
     static Value some(Interpreter&);
     static Value every(Interpreter&);
     static Value splice(Interpreter&);
+    static Value fill(Interpreter&);
 };
 
 }

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

@@ -0,0 +1,24 @@
+load("test-common.js");
+
+try {
+    assert(Array.prototype.fill.length === 1);
+
+    var array = [1, 2, 3, 4];
+    assertArrayEquals(array.fill(0, 2, 4), [1, 2, 0, 0]);
+    assertArrayEquals(array.fill(5, 1), [1, 5, 5, 5]);
+    assertArrayEquals(array.fill(6), [6, 6, 6, 6]);
+
+    assertArrayEquals([1, 2, 3].fill(4), [4, 4, 4]);
+    assertArrayEquals([1, 2, 3].fill(4, 1), [1, 4, 4]);
+    assertArrayEquals([1, 2, 3].fill(4, 1, 2), [1, 4, 3]);
+    assertArrayEquals([1, 2, 3].fill(4, 3, 3), [1, 2, 3]);
+    assertArrayEquals([1, 2, 3].fill(4, -3, -2), [4, 2, 3]);
+    assertArrayEquals([1, 2, 3].fill(4, NaN, NaN), [1, 2, 3]);
+    assertArrayEquals([1, 2, 3].fill(4, 3, 5), [1, 2, 3]);
+    assertArrayEquals(Array(3).fill(4), [4, 4, 4]);
+
+    console.log("PASS");
+} catch (e) {
+    console.log("FAIL: " + e);
+}
+

Libraries/LibJS/Tests/test-common.js

@@ -50,6 +50,21 @@ function assertThrowsError(testFunction, options) {
     }
 }
 
+/**
+ * Ensures the provided arrays contain exactly the same items.
+ * @param {Array} a First array
+ * @param {Array} b Second array
+ */
+function assertArrayEquals(a, b) {
+    if (a.length != b.length)
+        throw new AssertionError("Array lengths do not match");
+    
+    for (var i = 0; i < a.length; i++) {
+        if (a[i] !== b[i])
+            throw new AssertionError("Elements do not match");
+    }
+}
+
 const assertVisitsAll = (testFunction, expectedOutput) => {
     const visited = [];
     testFunction(value => visited.push(value));