The scripts requires its scripts to be written as modules. The idea behind modules is to specify which information inside a script should be made available to other scripts. In addition the module systems helps making it apparent which information inside a script is taken from other scripts.
A module basically consists of two types of operations: module includes and module exports.
Module Includes
A module include is required to use code defined in another module. There are two types of module includes: the default include and the named include.
Default Include
Whenever an included module should be used as a single object, like a class object, it should be included using a default include.
A default include assigns an included module to a variable:
const Module = include("module.id");
// do something with module
The assigned variable will contain the value that has been assigned to the default export of the included module.
Named Include
In other cases a single module exports multiple values, which can be used independently from each other. In such situations the different values can be included using a named include. A named include allows the selection of only a subset of the exported values to be included:
const { foo, bar, x, y } = include("module.id");
// do something with foo, bar, x and y
The included values can be any kind of object like functions, classes or constants.
Module Exports
To allow other modules to include values from another module, the module needs to first export it.
An export statement specifies as a form of contract that a value should be exported to other modules and therefore be used by the other modules.
Values are exported by assigning them to the module variable which is made available when executing the module script.
A module can contain two types export statements: a single default export or multiple named exports.
Named Exports
In some cases a module will need to export multiple values.
In such situations named exports can be used.
A named export assigns each exported value to its own variable of the module variable:
module.foo = function() {
...
};
module.bar = function(input) {
...
};
module.x = // exported value
module.y = // other exported value
The previous example module exports four values: foo, bar, x and y, which can be included using the code shown in the Named Include section.
Default Export
Often a module will only export a single value. In such situations a default export can be used to make the value accessible by other modules. A single value can be exported by using:
module.default = // value to export
The single exported default value needs to be assigned to the default value of the module variable.
This defines the value as the default export of the module.
A module can either use a single default export or multiple named exports. When a module uses both export types the default export is applied.