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diff --git a/js/src/frontend/ExpressionStatementEmitter.h b/js/src/frontend/ExpressionStatementEmitter.h
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+++ b/js/src/frontend/ExpressionStatementEmitter.h
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+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*-
+ * vim: set ts=8 sts=2 et sw=2 tw=80:
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef frontend_ExpressionStatementEmitter_h
+#define frontend_ExpressionStatementEmitter_h
+
+#include "mozilla/Attributes.h"
+
+#include <stdint.h>
+
+#include "frontend/ValueUsage.h"
+
+namespace js {
+namespace frontend {
+
+struct BytecodeEmitter;
+
+// Class for emitting bytecode for expression statement.
+//
+// Usage: (check for the return value is omitted for simplicity)
+//
+//   `expr;`
+//     // IgnoreValue if this is in normal script.
+//     // WantValue if this is in eval script.
+//     ValueUsage valueUsage = ...;
+//
+//     ExpressionStatementEmitter ese(this, valueUsage);
+//     ese.prepareForExpr(offset_of_expr);
+//     emit(expr);
+//     ese.emitEnd();
+//
+class MOZ_STACK_CLASS ExpressionStatementEmitter {
+  BytecodeEmitter* bce_;
+
+#ifdef DEBUG
+  // The stack depth before emitting expression.
+  int32_t depth_;
+#endif
+
+  // The usage of the value of the expression.
+  ValueUsage valueUsage_;
+
+#ifdef DEBUG
+  // The state of this emitter.
+  //
+  // +-------+ prepareForExpr +------+ emitEnd +-----+
+  // | Start |--------------->| Expr |-------->| End |
+  // +-------+                +------+         +-----+
+  enum class State {
+    // The initial state.
+    Start,
+
+    // After calling prepareForExpr.
+    Expr,
+
+    // After calling emitEnd.
+    End
+  };
+  State state_ = State::Start;
+#endif
+
+ public:
+  ExpressionStatementEmitter(BytecodeEmitter* bce, ValueUsage valueUsage);
+
+  // Parameters are the offset in the source code for each character below:
+  //
+  //   expr;
+  //   ^
+  //   |
+  //   beginPos
+  [[nodiscard]] bool prepareForExpr(uint32_t beginPos);
+  [[nodiscard]] bool emitEnd();
+};
+
+}  // namespace frontend
+}  // namespace js
+
+#endif /* frontend_ExpressionStatementEmitter_h */