Index: Grammar.y
===================================================================
--- Grammar.y	(revision 43818)
+++ Grammar.y	(working copy)
@@ -193,7 +193,7 @@
 
 /* keywords */
 %token BREAK CASE DEFAULT FOR NEW VAR CONSTTOKEN CONTINUE
-%token FUNCTION RETURN VOIDTOKEN DELETETOKEN
+%token FUNCTION RETURN YIELD VOIDTOKEN DELETETOKEN
 %token IF THISTOKEN DO WHILE INTOKEN INSTANCEOF TYPEOF
 %token SWITCH WITH RESERVED
 %token THROW TRY CATCH FINALLY
@@ -249,6 +249,7 @@
 %type <expressionNode>  LogicalORExpr LogicalORExprNoIn LogicalORExprNoBF
 %type <expressionNode>  ConditionalExpr ConditionalExprNoIn ConditionalExprNoBF
 %type <expressionNode>  AssignmentExpr AssignmentExprNoIn AssignmentExprNoBF
+%type <expressionNode>  YieldExpr YieldExprNoIn
 %type <expressionNode>  Expr ExprNoIn ExprNoBF
 
 %type <expressionNode>  ExprOpt ExprNoInOpt
@@ -256,7 +257,7 @@
 %type <statementNode>   Statement Block
 %type <statementNode>   VariableStatement ConstStatement EmptyStatement ExprStatement
 %type <statementNode>   IfStatement IterationStatement ContinueStatement
-%type <statementNode>   BreakStatement ReturnStatement WithStatement
+%type <statementNode>   BreakStatement ReturnStatement YieldStatement WithStatement
 %type <statementNode>   SwitchStatement LabelledStatement
 %type <statementNode>   ThrowStatement TryStatement
 %type <statementNode>   DebuggerStatement
@@ -743,6 +744,11 @@
                                         { $$ = createNodeInfo<ExpressionNode*>(makeAssignNode(GLOBAL_DATA, $1.m_node, $2, $3.m_node, $1.m_features & AssignFeature, $3.m_features & AssignFeature, 
                                                                                                      @1.first_column, @2.first_column + 1, @3.last_column), $1.m_features | $3.m_features | AssignFeature, $1.m_numConstants + $3.m_numConstants); 
                                         }
+  | LeftHandSideExpr AssignmentOperator YieldExpr
+                                        { $$ = createNodeInfo<ExpressionNode*>(makeAssignNode(GLOBAL_DATA, $1.m_node, $2, $3.m_node, $1.m_features & AssignFeature, $3.m_features & AssignFeature, 
+                                                                                                     @1.first_column, @2.first_column + 1, @3.last_column), $1.m_features | $3.m_features | AssignFeature, $1.m_numConstants + $3.m_numConstants); 
+                                        }
+  | '(' YieldExpr ')'                   { $$ = $2; }
 ;
 
 AssignmentExprNoIn:
@@ -751,6 +757,11 @@
                                         { $$ = createNodeInfo<ExpressionNode*>(makeAssignNode(GLOBAL_DATA, $1.m_node, $2, $3.m_node, $1.m_features & AssignFeature, $3.m_features & AssignFeature, 
                                                                                                      @1.first_column, @2.first_column + 1, @3.last_column), $1.m_features | $3.m_features | AssignFeature, $1.m_numConstants + $3.m_numConstants);
                                         }
+  | LeftHandSideExpr AssignmentOperator YieldExprNoIn
+                                        { $$ = createNodeInfo<ExpressionNode*>(makeAssignNode(GLOBAL_DATA, $1.m_node, $2, $3.m_node, $1.m_features & AssignFeature, $3.m_features & AssignFeature, 
+                                                                                                     @1.first_column, @2.first_column + 1, @3.last_column), $1.m_features | $3.m_features | AssignFeature, $1.m_numConstants + $3.m_numConstants);
+                                        }
+  | '(' YieldExpr ')'                   { $$ = $2; }
 ;
 
 AssignmentExprNoBF:
@@ -759,8 +770,23 @@
                                         { $$ = createNodeInfo<ExpressionNode*>(makeAssignNode(GLOBAL_DATA, $1.m_node, $2, $3.m_node, $1.m_features & AssignFeature, $3.m_features & AssignFeature,
                                                                                                      @1.first_column, @2.first_column + 1, @3.last_column), $1.m_features | $3.m_features | AssignFeature, $1.m_numConstants + $3.m_numConstants); 
                                         }
+  | LeftHandSideExprNoBF AssignmentOperator YieldExpr
+                                        { $$ = createNodeInfo<ExpressionNode*>(makeAssignNode(GLOBAL_DATA, $1.m_node, $2, $3.m_node, $1.m_features & AssignFeature, $3.m_features & AssignFeature,
+                                                                                                     @1.first_column, @2.first_column + 1, @3.last_column), $1.m_features | $3.m_features | AssignFeature, $1.m_numConstants + $3.m_numConstants); 
+                                        }
+  | '(' YieldExpr ')'                   { $$ = $2; }
 ;
 
+YieldExpr:
+    YIELD
+  | YIELD AssignmentExpr
+;
+
+YieldExprNoIn:
+    YIELD
+  | YIELD AssignmentExprNoIn
+;
+
 AssignmentOperator:
     '='                                 { $$ = OpEqual; }
   | PLUSEQUAL                           { $$ = OpPlusEq; }
@@ -803,6 +829,7 @@
   | ContinueStatement
   | BreakStatement
   | ReturnStatement
+  | YieldStatement
   | WithStatement
   | SwitchStatement
   | LabelledStatement
@@ -1069,6 +1096,15 @@
                                           $$ = createNodeDeclarationInfo<StatementNode*>(node, 0, 0, $2.m_features, $2.m_numConstants); DBG($$.m_node, @1, @2); AUTO_SEMICOLON; }
 ;
 
+YieldStatement:
+    YieldExpr ';'                       { ReturnNode* node = new (GLOBAL_DATA) ReturnNode(GLOBAL_DATA, 0); 
+                                          SET_EXCEPTION_LOCATION(node, @1.first_column, @1.last_column, @1.last_column); 
+                                          $$ = createNodeDeclarationInfo<StatementNode*>(node, 0, 0, 0, 0); DBG($$.m_node, @1, @2); }
+  | YieldExpr error                     { ReturnNode* node = new (GLOBAL_DATA) ReturnNode(GLOBAL_DATA, 0); 
+                                          SET_EXCEPTION_LOCATION(node, @1.first_column, @1.last_column, @1.last_column); 
+                                          $$ = createNodeDeclarationInfo<StatementNode*>(node, 0, 0, 0, 0); DBG($$.m_node, @1, @1); AUTO_SEMICOLON; }
+;
+
 WithStatement:
     WITH '(' Expr ')' Statement         { $$ = createNodeDeclarationInfo<StatementNode*>(new (GLOBAL_DATA) WithNode(GLOBAL_DATA, $3.m_node, $5.m_node, @3.last_column, @3.last_column - @3.first_column),
                                                                                          $5.m_varDeclarations, $5.m_funcDeclarations, $3.m_features | $5.m_features | WithFeature, $3.m_numConstants + $5.m_numConstants);
@@ -1577,16 +1613,19 @@
 AssignmentExpr_NoNode:
     ConditionalExpr_NoNode
   | LeftHandSideExpr_NoNode AssignmentOperator_NoNode AssignmentExpr_NoNode
+  | LeftHandSideExpr_NoNode AssignmentOperator_NoNode YieldExpr_NoNode
 ;
 
 AssignmentExprNoIn_NoNode:
     ConditionalExprNoIn_NoNode
   | LeftHandSideExpr_NoNode AssignmentOperator_NoNode AssignmentExprNoIn_NoNode
+  | LeftHandSideExpr_NoNode AssignmentOperator_NoNode YieldExprNoIn_NoNode
 ;
 
 AssignmentExprNoBF_NoNode:
     ConditionalExprNoBF_NoNode
   | LeftHandSideExprNoBF_NoNode AssignmentOperator_NoNode AssignmentExpr_NoNode
+  | LeftHandSideExprNoBF_NoNode AssignmentOperator_NoNode YieldExpr_NoNode
 ;
 
 AssignmentOperator_NoNode:
@@ -1604,6 +1643,16 @@
   | MODEQUAL
 ;
 
+YieldExpr_NoNode:
+    YIELD
+  | YIELD AssignmentExpr_NoNode
+;
+
+YieldExprNoIn_NoNode:
+    YIELD
+  | YIELD AssignmentExprNoIn_NoNode
+;
+
 Expr_NoNode:
     AssignmentExpr_NoNode
   | Expr_NoNode ',' AssignmentExpr_NoNode
@@ -1631,6 +1680,7 @@
   | ContinueStatement_NoNode
   | BreakStatement_NoNode
   | ReturnStatement_NoNode
+  | YieldStatement_NoNode
   | WithStatement_NoNode
   | SwitchStatement_NoNode
   | LabelledStatement_NoNode
@@ -1742,6 +1792,11 @@
   | RETURN Expr_NoNode error { AUTO_SEMICOLON; }
 ;
 
+YieldStatement_NoNode:
+    YieldExpr_NoNode ';'
+  | YieldExpr_NoNode error { AUTO_SEMICOLON; }
+;
+
 WithStatement_NoNode:
     WITH '(' Expr_NoNode ')' Statement_NoNode
 ;
Index: Keywords.table
===================================================================
--- Keywords.table	(revision 43818)
+++ Keywords.table	(working copy)
@@ -20,6 +20,7 @@
 continue	CONTINUE
 function	FUNCTION
 return		RETURN
+yield		YIELD
 void		VOIDTOKEN
 delete		DELETETOKEN
 if		IF
Index: Lexer.cpp
===================================================================
--- Lexer.cpp	(revision 43818)
+++ Lexer.cpp	(working copy)
@@ -212,7 +212,7 @@
 
 inline bool Lexer::lastTokenWasRestrKeyword() const
 {
-    return m_lastToken == CONTINUE || m_lastToken == BREAK || m_lastToken == RETURN || m_lastToken == THROW;
+    return m_lastToken == CONTINUE || m_lastToken == BREAK || m_lastToken == RETURN || m_lastToken == THROW || m_lastToken == YIELD;
 }
 
 static NEVER_INLINE bool isNonASCIIIdentStart(int c)