2.1.24 [ECMA-262/6] Section 12.14.1 Static Semantics: Early Errors

V0053: It is an early Syntax Error if LeftHandSideExpression is an immutable binding reference

The specification states:

 12.14.1 Static Semantics: Early Errors
  
     AssignmentExpression : LeftHandSideExpression = AssignmentExpression
  
         • It is a Syntax Error if LeftHandSideExpression is either an ObjectLiteral or an 
         ArrayLiteral and the lexical token sequence matched by LeftHandSideExpression 
         cannot be parsed with no tokens left over using AssignmentPattern as the goal 
         symbol.
  
         • It is an early Reference Error if LeftHandSideExpression is neither an 
         ObjectLiteral nor an ArrayLiteral and IsValidSimpleAssignmentTarget of 
         LeftHandSideExpression is false.
  
     AssignmentExpression : LeftHandSideExpression AssignmentOperator AssignmentExpression
  
         • It is an early Reference Error if IsValidSimpleAssignmentTarget of 
         LeftHandSideExpression is false.

IE11 Mode (All versions)

It is an early Syntax Error if LeftHandSideExpression is an immutable binding reference.