Branches Tags. Could not load branches. Could not load tags. Latest commit. Remove deprecated method SourceFile. Git stats 17, commits. Failed to load latest commit information. View code. Getting Started The easiest way to install the compiler is with NPM or Yarn : yarn global add google-closure-compiler OR npm i -g google-closure-compiler. Use single-quotes, so that bash doesn't try to expand the '! About A JavaScript checker and optimizer. Code of conduct. Releases tags.
Packages 0 No packages published. You signed in with another tab or window. Reload to refresh your session. Or an unused variable, even though you set a value for it later? Depending on the complexity of your models, or how you expose your objects to the external world, this can lead to unwanted situations.
Those structures that were unused were automatically identified and removed by Closure Compiler. Plus, local variables let and constants const are substituted by var declarations.
What about a scenario in which one flow depends on another conditional flow? The conditional flow was analyzed and reprogrammed to one single line. This operator says that only if the first condition is true will the second be executed. Otherwise, if our random number is not equal to 1, then b will never receive "abc" as value. The conditional if s were nested. It can be potentially dangerous and unproductive to always review the code that was compiled. Also, what happens if you want to keep the check function globally available to other JavaScript files?
The typing system of what Closure Compiler checks is the heart of the whole thing. You can annotate your code to be more typed, which means Compiler will check for wrong usages based on your annotations. You need your param to be a number in all cases, so you can ask Closure Compiler to check if a caller is passing anything different than that:.
This is largely because the decision to use a particular Closure tool is made by an individual engineering team at Google, so there is no guarantee that a team that is using the Compiler is also using the Library.
Now that Closure is more mature, the main reason to adopt one tool but not another is because of a dependency on legacy code that already depends on a similar tool. You may find yourself in a similar situation when deciding how best to incorporate Closure into an existing project.
Nevertheless, even though it is possible to compile jQuery with the Compiler or to use Templates to create functions that can be called from Dojo, the entire Closure suite should be adopted to achieve the maximum benefit from the tools. It is indeed the case with Closure that the whole is greater than the sum of its parts. For example, although the Library and the Compiler can be used independently, they are only moderately effective when used on their own.
In some cases, the Library is outright unusable without the Compiler see datetimesymbols. Both must be used together in order to get the most out of Closure. Currently, each tool in the Closure suite must be downloaded and installed separately.
As the tools are independent of one another, each is maintained as its own project on code. Unfortunately, the Closure Library does not offer such a bundle, so the only way to get the code is to check it out of the Subversion repository associated with the project.
Because all of the Closure Tools are designed to be used independently, it takes a bit of effort to get them set up and working together. Fortunately, Appendix C introduces plovr , which is a single build tool that integrates all of the Closure Tools in a single download the code for all of the Closure Tools is included in the plovr jar. Using plovr eliminates the need for many of the scripts required to build the example in the following section, as well as the dependency on Python.
At the time of this writing, the tools also lack version numbers with the exception of the Closure Inspector. Because each is stored in Subversion, they do have revision numbers , but those are simply incremented every time a change is checked in. This is less significant than a version number, which is an explicit branding that generally reflects achieving a particular milestone or achieving some level of stability. Fortunately, each project has a number of tests to prevent regressions in new releases.
Therefore, although all of the examples in this book were created using the Closure Tools built from the revision numbers listed in Table , it is probably safe to use the latest version of each tool to reproduce the results in the examples. This section will walk through downloading and configuring each tool, whereas the next section will provide a comprehensive code example that will demonstrate how each is used.
If you are a Mac or Linux user, this section expects that you are familiar with the Terminal and have Subversion installed. Mac users should have Subversion installed by default, but Linux users may have to run sudo apt-get install svn to get it apt-get is used to install packages on Ubuntu and Debian, so the package management system of your Linux distribution may differ.
In either case, running which svn in the Terminal will print the location of the Subversion executable if it is installed. If you are a Windows user, you will need to install Subversion if you have not done so already. This means that it can be used on Windows without using the Command Prompt. Many of the examples in this book include commands that can be run from a terminal on Mac or Linux.
When using Cygwin, the shell scripts in this book that are designed for Mac and Linux can be run as-is. For simplicity, each directory name will match the project name on code. As mentioned at the beginning of this section, the Closure Library cannot be downloaded as a zip file, so it must be downloaded by checking the code out of Subversion. Mac and Linux users can run the following commands from Terminal to download the Closure Library:.
The primary binary for Closure Templates is used to compile templates into JavaScript. It is also fairly easy to build the Templates binary from source. It is also fairly easy to build the Compiler from source. The Compiler can then be built using Apache Ant:. This will prompt you to install the extension. This section will walk through a simple example to demonstrate how all of the Closure Tools can be used together.
Before following the instructions in this section, make sure all of the Tools are installed as described in the previous section. A simple web search should yield appropriate instructions for installing Java and Python on your computer if you do not have them already.
The first step will exercise the Closure Library by creating a web page that loads the kernel of the Library and then some of its DOM utilities to insert the text Hello World! Assuming you have all of the tools checked out as described in the previous section, first create a subdirectory of your closure directory named hello-world.
Then create the following file named hello. In the same directory, also create a file named hello. Open hello. The details of how goog. This may seem like a lot of code to load in order to do the equivalent of document. In the hello-world directory, create a new file named hello. This should generate a file named hello. Now update hello. In order to use hello. Now loading hello. Although everything is working, maintaining these dependencies manually is very tedious.
Fortunately, the Closure Library contains a Python script named calcdeps. The hello-deps. The details of how calcdeps. To make sure that your dependencies are loading correctly, verify that loading hello.
To minimize the risk of this sort of name collision, use the Closure Library's goog. For example, the notes application uses Note objects created by a Note constructor function.
If any other JavaScript file defines a global Note function or variable, it could overwrite this constructor. Therefore the example creates a namespace for this constructor with the following call to goog. The goog. It checks to see whether each object property in the path expression exists, and if it doesn't exist it initializes it.
The above function call is equivalent to:. Because goog. Note that goog. See Using the Dependency Calculation Script to learn how to use calcdeps. Once the tutorial. Note object structure exists, the example assigns the constructor function to the Note property. The Note constructor is now in the tutorial. This method uses the Closure Library function goog.
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