Why encapsulate module in function? [duplicate]

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• What is the (function() { } )() construct in JavaScript? 17 answers

So I'm reading some node.js-modules in a school example app, and they are all instantiated in a function like this:

(function() {
    "use strict";

    // Some declarations

    module.exports = some value;
}());

That is, they are all encapsulated by an anonymous function like this:

(function() {
    // Module
}());

Does anyone know what the purpose may be for doing so? Has it something to do with efficiency?

via Jesper