Wrap your code in an immediately invoked function expression (IFFE). It runs immediately when you create it and has no name. Normally you would create a IFFE like this:
(function() {
// your code
}());
It is common practice to remove the outer wrapping parenthesis and use a ! or + at the start of the anonymous function:
!function() {
function foo() {
console.log('foobar');
};
foo();
}();
You can pass a variable into the IFFE so that it can be used within its local scope. Here I am passing in the underscore library using _ to be used within the module.
!function(underscore) {
console.log(underscore.VERSION);
}(_);
You can name the passed in variable (parameter) whatever you like so while you would normally use the underscore library by using _ you can now use it within the local scope using underscore. variable.
Another use might be to pass in the window object and create a variable called global within your IFFE. Now you can access the global scope by using the global variable.
var bar = "foo";
!function(global) {
console.log(global.bar); // foo
}(window);