The strict mode restriction and exceptions
The identifiers "implements
", "interface
", "let
", "package
",
"private
", "protected
", "public
", "static
", and "yield
" are
classified as FutureReservedWord tokens within strict mode code. (7.6.12).
A conforming implementation, when processing strict mode code, may not extend the syntax of NumericLiteral (7.8.3) to include OctalIntegerLiteral as described in B.1.1.
A conforming implementation, when processing strict mode code (see 10.1.1), may not extend the syntax of EscapeSequence to include OctalEscapeSequence as described in B.1.2.
Assignment to an undeclared identifier or otherwise unresolvable reference does not create a property in the global
object. When a simple assignment occurs within strict mode code, its LeftHandSide must not
evaluate to an unresolvable Reference. If it does a ReferenceError exception is thrown (8.7.2). The LeftHandSide also may not be a reference to a data property with the attribute
value {[[Writable]]:false}, to an accessor property with the attribute value {[[Set]]:undefined}, nor to a
non-existent property of an object whose [[Extensible]] internal property has the value false. In these cases a
TypeError
exception is thrown (11.13.1).
The identifier eval
or arguments
may not appear as the LeftHandSideExpression of an
Assignment operator (11.13) or of a PostfixExpression (11.3) or as
the UnaryExpression operated upon by a Prefix Increment (11.4.4) or a Prefix Decrement (11.4.5) operator.
Arguments objects for strict mode functions define non-configurable accessor properties named "caller
" and
"callee
" which throw a TypeError exception on access (10.6).
Arguments objects for strict mode functions do not dynamically share their array indexed property values with the corresponding formal parameter bindings of their functions. (10.6).
For strict mode functions, if an arguments object is created the binding of the local identifier arguments
to the arguments object is immutable and hence may not be the target of an assignment expression. (10.5).
It is a SyntaxError if strict mode code contains an ObjectLiteral with more than one definition of any data property (11.1.5).
It is a SyntaxError if the Identifier "eval"
or the Identifier "arguments"
occurs as the Identifier in a PropertySetParameterList of a PropertyAssignment that is contained in strict code or if its
FunctionBody is strict code (11.1.5).
Strict mode eval code cannot instantiate variables or functions in the variable environment of the caller to eval. Instead, a new variable environment is created and that environment is used for declaration binding instantiation for the eval code (10.4.2).
If this is evaluated within strict mode code, then the this value is not coerced
to an object. A this value of null or undefined is not converted to the global object and primitive
values are not converted to wrapper objects. The this value passed via a function call (including calls made using
Function.prototype.apply
and Function.prototype.call) do not
coerce the passed this value to an object (10.4.3, 11.1.1, 15.3.4.3, 15.3.4.4).
When a delete
operator occurs within strict mode code, a SyntaxError is
thrown if its UnaryExpression is a direct reference to a variable, function argument, or function name(11.4.1).
When a delete
operator occurs within strict mode code, a TypeError is
thrown if the property to be deleted has the attribute { [[Configurable]]:false } (11.4.1).
It is a SyntaxError if a VariableDeclaration or VariableDeclarationNoIn occurs within strict code and its Identifier is eval
or arguments
(12.2.1).
Strict mode code may not include a WithStatement. The occurrence of a WithStatement in such a context is an SyntaxError (12.10).
It is a SyntaxError if a TryStatement with a Catch occurs within
strict code and the Identifier of the Catch
production is eval
or arguments
(12.14.1)
It is a SyntaxError if the identifier eval
or arguments
appears within a FormalParameterList of a strict mode FunctionDeclaration or FunctionExpression (13.1)
A strict mode function may not have two or more formal parameters that have the same name. An attempt to create such a
function using a FunctionDeclaration, FunctionExpression, or Function
constructor is a
SyntaxError (13.1, 15.3.2).
An implementation may not extend, beyond that defined in this specification, the meanings within strict mode functions of
properties named caller
or arguments
of function instances. ECMAScript code may not create or
modify properties with these names on function objects that correspond to strict mode functions (10.6, 13.2, 15.3.4.5.3).
It is a SyntaxError to use within strict mode code the identifiers eval
or
arguments
as the Identifier of a FunctionDeclaration or FunctionExpression or as a formal
parameter name (13.1). Attempting to dynamically define such a strict mode function using the
Function
constructor (15.3.2) will throw a SyntaxError exception.