Basic Module Pattern JavaScript

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);