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diff --git a/src/mongo/db/pipeline/expression_javascript.h b/src/mongo/db/pipeline/expression_javascript.h
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+/**
+ *    Copyright (C) 2019-present MongoDB, Inc.
+ *
+ *    This program is free software: you can redistribute it and/or modify
+ *    it under the terms of the Server Side Public License, version 1,
+ *    as published by MongoDB, Inc.
+ *
+ *    This program is distributed in the hope that it will be useful,
+ *    but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *    Server Side Public License for more details.
+ *
+ *    You should have received a copy of the Server Side Public License
+ *    along with this program. If not, see
+ *    <http://www.mongodb.com/licensing/server-side-public-license>.
+ *
+ *    As a special exception, the copyright holders give permission to link the
+ *    code of portions of this program with the OpenSSL library under certain
+ *    conditions as described in each individual source file and distribute
+ *    linked combinations including the program with the OpenSSL library. You
+ *    must comply with the Server Side Public License in all respects for
+ *    all of the code used other than as permitted herein. If you modify file(s)
+ *    with this exception, you may extend this exception to your version of the
+ *    file(s), but you are not obligated to do so. If you do not wish to do so,
+ *    delete this exception statement from your version. If you delete this
+ *    exception statement from all source files in the program, then also delete
+ *    it in the license file.
+ */
+
+#pragma once
+
+#include "mongo/db/pipeline/expression.h"
+#include "mongo/db/pipeline/javascript_execution.h"
+
+/**
+ * This file contains all expressions which make use of JavaScript execution and depend on the JS
+ * engine to operate.
+ */
+namespace mongo {
+
+/**
+ * This expression takes in a JavaScript function and a "this" reference, and returns an array of
+ * key/value objects which are the results of calling emit() from the provided JS function.
+ */
+class ExpressionInternalJsEmit final : public Expression {
+public:
+    Value evaluate(const Document& root, Variables* variables) const final;
+    static boost::intrusive_ptr<Expression> parse(
+        const boost::intrusive_ptr<ExpressionContext>& expCtx,
+        BSONElement expr,
+        const VariablesParseState& vps);
+    Value serialize(bool explain) const final;
+
+    void acceptVisitor(ExpressionVisitor* visitor) final {
+        return visitor->visit(this);
+    }
+
+private:
+    const boost::intrusive_ptr<Expression>& _thisRef;
+
+    ExpressionInternalJsEmit(const boost::intrusive_ptr<ExpressionContext>& expCtx,
+                             boost::intrusive_ptr<Expression> thisRef,
+                             std::string funcSourceString);
+
+    // Vector needs to be a member on the class so that it can be attached to the JS scope in the
+    // constructor and stay alive through the lifetime of the Expression object.
+    std::vector<BSONObj> _emittedObjects{};
+
+    void _doAddDependencies(DepsTracker* deps) const final override;
+
+    std::string _funcSource;
+    ScriptingFunction _func;
+
+    static constexpr auto kExpressionName = "$_internalJsEmit"_sd;
+};
+}  // namespace mongo