text: This Hello World exercise introduces the process of using the Closure Library in a web page. To do this exercise you need to have some familiarity with JavaScript, as well as a Git client. You may already have a Git client. You can tell whether you have Git client by trying to execute the command in step 1.
  Hello Closure
  To get started with the Closure Library, use Closure JavaScript functions in a simple web page by following these steps:
  Step 1: Download the Closure Library
  Download the Closure Library from the Git repository by executing the following command from the command line:
  git clone
  You need a Git client to execute this command, but you may already have one. Try the command, and if it doesn't work download and install a Git client.
  After executing this command you should have a directory
  named
  closure-library that contains the Closure
  Library code.
  Step 2: Create a JavaScript file that uses the Closure Library
  Save the following JavaScript in a file
  called
  hello.js. Place this file next to
  the
  closure-library directory.
  goog.require('goog.dom'); goog.require('goog.dom.TagName'); function sayHi() { var newHeader = goog.dom.createDom(goog.dom.TagName.H1, {'style': 'background-color:#EEE'}, 'Hello world!'); goog.dom.appendChild(document.body, newHeader); }
  Step 3: Create an HTML file
  Save the following HTML in a file
  called
  hello.html. Place this file next to
  the
  closure-library directory and
  the
  hello.js file.
  <html> <head> <script src="closure-library/closure/goog/base.js"></script> <script src="hello.js"></script> </head> <body onload="sayHi()"> </body> </html>
  Step 4: Say Hello to the Closure Library
  Open the HTML file in a browser. You should see the words "Hello world!":
  How Does This Example Work?
  The
  hello.js JavaScript uses two functions it doesn't
  define:
  goog.dom.createDom()
  and
  goog.dom.appendChild(). Where do these functions come
  from?
  These functions are defined in the Closure Library that you downloaded
  in
  Step 1, in the
  file
  closure-library/dom/dom.js.
  To make use of these functions, the example does two things:
  - It includes the statement
  goog.require('goog.dom')at the beginning of the JavaScript in Step 2.
  - It includes the Closure Library bootstrap file
  base.jsin the HTML in Step 3.
  The
  base.js file defines the
  function
  goog.require(). The function
  call
  goog.require('goog.dom') loads the JavaScript file
  that defines the functions in the
  goog.dom namespace,
  along with any other files from the Closure Library that those functions
  need.
  The Closure Library loads these files by dynamically adding a script
  tag to the document for each needed Closure Library file. So, for example, the
  statement
  goog.require('goog.dom') causes the following
  tag to be added to the document, where
  path-to-closure is
  the path from the HTML file to the directory that
  contains
  base.js:
  <script src="path-to-closure/dom/dom.js"></script>
  Typically a single
  goog.require() statement will load
  only a fraction of the Closure Library codebase.
  Note: Do not put your
  goog.require() statements
  in the same script tag as the entry point to code that uses
  the
  goog.required functions or
  classes. A
  goog.require() call adds code to the
  document after the script tag containing the call. For
  example, this code works:
  <script src="closure-library/closure/goog/base.js"></script> <script> goog.require('goog.dom'); </script> <script> var newHeader = goog.dom.createDom(goog.dom.TagName.H1); </script>
  The
  goog.require() call adds the code
  for
  goog.dom.createDom() immediately before the script
  tag containing the line
  var newHeader =
  goog.dom.createDom(goog.dom.TagName.H1).
  In contrast, the following code produces an error:
  <script src="closure-library/closure/goog/base.js"></script> <script> // DON'T DO THIS. goog.require('goog.dom'); var newHeader = goog.dom.createDom(goog.dom.TagName.H1); </script>
  This
  goog.require() call adds the code
  for
  goog.dom.createDom() in a script tag that won't be
  interpreted until after a call to
  goog.dom.createDom()
  has already been made.
  Note that this restriction does not apply when you use ClosureBuilder.
  Including
  base.js isn't the only way to include Closure
  Library code, but it is the easiest way to get started. No matter how
  you grab Closure Library code, however, you will always
  use
  goog.require() to declare the parts of the Closure
  Library that you need.
  Next Steps
  This example illustrates one way of getting just the parts of the
  Closure Library that you need: including
  base.js in your
  web page and calling its function
  goog.require().
  The Closure Library also provides a tool for assembling just the parts of the library you need into a single JavaScript file. To find out more about this tool, read Using ClosureBuilder.