TypeScript Language Specification v1.5

where ModuleName is the name of the module and ModuleStatements is the code generated for the
statements in the module body. The ModuleName function parameter may be prefixed with one or more
underscore characters to ensure the name is unique within the function body. Note that the entire module
is emitted as an anonymous function that is immediately executed. This ensures that local variables are in
their own lexical environment isolated from the surrounding context. Also note that the generated
function doesn't create and return a module instance, but rather it extends the existing instance (which
may have just been created in the function call). This ensures that internal modules can extend each other.
An import statement generates code of the form
var = ;
This code is emitted only if the imported entity is referenced as a PrimaryExpression somewhere in the
body of the importing module. If an imported entity is referenced only as a TypeName or ModuleName,
nothing is emitted. This ensures that types declared in one internal module can be referenced through an
import alias in another internal module with no run-time overhead.
When a variable is exported, all references to the variable in the body of the module are replaced with
.
This effectively promotes the variable to be a property on the module instance and ensures that all
references to the variable become references to the property.
When a function, class, enum, or module is exported, the code generated for the entity is followed by an
assignment statement of the form
. = ;
This copies a reference to the entity into a property on the module instance.
142