LibJS: Add Array.prototype.unshift()

Author: https://github.com/linusg
Commit: https://github.com/SerenityOS/serenity/commit/29253bf9325
Pull-request: https://github.com/SerenityOS/serenity/pull/1793

Libraries/LibJS/Runtime/ArrayPrototype.cpp

@@ -41,6 +41,7 @@ ArrayPrototype::ArrayPrototype()
     put_native_function("push", push, 1);
     put_native_function("shift", shift, 0);
     put_native_function("toString", to_string, 0);
+    put_native_function("unshift", unshift, 1);
     put("length", Value(0));
 }
 
@@ -70,6 +71,16 @@ Value ArrayPrototype::push(Interpreter& interpreter)
     return Value(array->length());
 }
 
+Value ArrayPrototype::unshift(Interpreter& interpreter)
+{
+    auto* array = array_from(interpreter);
+    if (!array)
+        return {};
+    for (size_t i = 0; i < interpreter.argument_count(); ++i)
+        array->elements().insert(i, interpreter.argument(i));
+    return Value(array->length());
+}
+
 Value ArrayPrototype::pop(Interpreter& interpreter)
 {
     auto* array = array_from(interpreter);

Libraries/LibJS/Runtime/ArrayPrototype.h

@@ -42,6 +42,7 @@ private:
     static Value push(Interpreter&);
     static Value shift(Interpreter&);
     static Value to_string(Interpreter&);
+    static Value unshift(Interpreter&);
 };
 
 }

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

@@ -0,0 +1,30 @@
+load("test-common.js");
+
+try {
+    assert(Array.prototype.unshift.length === 1);
+
+    var a = ["hello"];
+    var length = a.unshift();
+    assert(length === 1);
+    assert(a.length === 1);
+    assert(a[0] === "hello");
+
+    length = a.unshift("friends");
+    assert(length === 2);
+    assert(a.length === 2);
+    assert(a[0] === "friends");
+    assert(a[1] === "hello");
+
+    length = a.unshift(1, 2, 3);
+    assert(length === 5);
+    assert(a.length === 5);
+    assert(a[0] === 1);
+    assert(a[1] === 2);
+    assert(a[2] === 3);
+    assert(a[3] === "friends");
+    assert(a[4] === "hello");
+
+    console.log("PASS");
+} catch (e) {
+    console.log("FAIL: " + e);
+}