shorthand property name with *this*

Question

The following code fails

let x = {this}

Why I cannot use shorthand property name with this?

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error messages from browsers

chrome 66.0.3359.117 : Uncaught SyntaxError: Unexpected token }

firefox 59.0.1 : this is an invalid identifier

edge 41.16299.371.0 : The use of a keyword for an identifier is invalid

I don't quite get what these messages say.

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Just to make it clear, the following code runs fine

let x = 5
let y = {x}
let z = {this:this}

console.log({x,y,z})

Answer 1

According to the ECMA spec (I have put in bold what is important):

12.2.6 Object Initializer

NOTE 1 An object initializer is an expression describing the initialization of an Object, written in a form resembling a literal. It is a list of zero or more pairs of property keys and associated values, enclosed in curly brackets. The values need not be literals; they are evaluated each time the object initializer is evaluated.

Syntax

• ObjectLiteral[Yield] :
  • { }
  • { PropertyDefinitionList[?Yield] }
  • { PropertyDefinitionList[?Yield] , }
• PropertyDefinitionList[Yield] :
  • PropertyDefinition[?Yield]
  • PropertyDefinitionList[?Yield] , PropertyDefinition[?Yield]
• PropertyDefinition[Yield] :
  • IdentifierReference[?Yield]
  • CoverInitializedName[?Yield]
  • PropertyName[?Yield] : AssignmentExpression[In, ?Yield]
  • MethodDefinition[?Yield]
• PropertyName[Yield] :
  • LiteralPropertyName
  • ComputedPropertyName[?Yield]
• LiteralPropertyName :
  • IdentifierName
  • StringLiteral
  • NumericLiteral
• ComputedPropertyName[Yield] : -[ AssignmentExpression[In, ?Yield] ]
  • CoverInitializedName[Yield] :
  • IdentifierReference[?Yield] Initializer[In, ?Yield]
• Initializer[In, Yield] :
  • = AssignmentExpression[?In, ?Yield]

NOTE 2 MethodDefinition is defined in 14.3.

NOTE 3 In certain contexts, ObjectLiteral is used as a cover grammar for a more restricted secondary grammar. The CoverInitializedName production is necessary to fully cover these secondary grammars. However, use of this production results in an early Syntax Error in normal contexts where an actual ObjectLiteral is expected.

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12.1 Identifiers

Syntax

• IdentifierReference[Yield] :
  • Identifier
  • [~Yield] yield
• BindingIdentifier[Yield] :
  • Identifier
  • [~Yield] yield
• LabelIdentifier[Yield] :
  • Identifier
  • [~Yield] yield
• Identifier :
  • IdentifierName but not ReservedWord

What this means is that in the shorthand let x = {Identifier} does not permit reserved words as Identifier. And this is a reserved word, look at 11.6.2 Reserved Words and onward. On the other hand we see that the expanded way of writing it is different:
let x = {PropertyName:AssignmentExpression} where PropertName is either ComputedPropertyName or LiteralPropertyName wich is IdentifierName that does not exclude the reserved words. Thus let x = {this: this} or let x = {class: 10} is no problem. It does not, however, explain why this is so, maybe it would complicate the grammar or make it ambiguous?