TypeScript Language Specification v1.5

BindingProperty:
Identifier Initialiser opt
PropertyName : Identifier Initialiser opt
PropertyName : BindingPattern Initialiser opt
ArrayBindingPattern:
[ Elision opt BindingRestElement opt ]
[ BindingElementList ]
[ BindingElementList , Elision opt BindingRestElement opt ]
BindingElementList:
Elision opt BindingElement
BindingElementList , Elision opt BindingElement
BindingElement:
Identifier Initialiser opt
BindingPattern Initialiser opt
BindingRestElement:
... Identifier
Each binding property or element that specifies an identifier introduces a variable by that name. The type
of the variable is the widened form (section 3.11) of the type associated with the binding property or
element, as defined in the following.
The type T associated with a destructuring variable declaration is determined as follows:
If the declaration includes a type annotation, T is that type.
Otherwise, if the declaration includes an initializer expression, T is the type of that initializer
expression.
Otherwise, T is the Any type.
The type T associated with a binding property is determined as follows:
Let S be the type associated with the immediately containing destructuring variable declaration,
binding property, or binding element.
If S is the Any type:
o If the binding property specifies an initializer expression, T is the type of that initializer
expression.
o Otherwise, T is the Any type.
Let P be the property name specified in the binding property.
If S has an apparent property with the name P, T is the type of that property.
Otherwise, if S has a numeric index signature and P is a numerical name, T is the type of the
numeric index signature.
Otherwise, if S has a string index signature, T is the type of the string index signature.
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