Bundling and minification are two distinct performance optimizations you can apply in a web app. Used together, bundling and minification improve performance by reducing the number of server requests and reducing the size of the requested static assets.
Bundling and minification primarily improve the first page request load time. Once a web page has been requested, the browser caches the static assets (JavaScript, CSS, and images). Consequently, bundling and minification don't improve performance when requesting the same page, or pages, on the same site requesting the same assets. If the expires header isn't set correctly on the assets and if bundling and minification isn't used, the browser's freshness heuristics mark the assets stale after a few days. Additionally, the browser requires a validation request for each asset. In this case, bundling and minification provide a performance improvement even after the first page request.
Bundling combines multiple files into a single file. Bundling reduces the number of server requests which are necessary to render a web asset, such as a web page. You can create any number of individual bundles specifically for CSS, JavaScript, etc. Fewer files means fewer HTTP requests from the browser to the server or from the service providing your application. This results in improved first page load performance.
Minification removes unnecessary characters from code without altering functionality. The result is a significant size reduction in requested assets (such as CSS, images, and JavaScript files). Common side effects of minification include shortening variable names to one character and removing comments and unnecessary whitespace.
Browsers are fairly verbose with regard to HTTP request headers. The total bytes sent metric saw a significant reduction when bundling. The load time shows a significant improvement, however this example ran locally. Greater performance gains are realized when using bundling and minification with assets transferred over a network.
The MVC and Razor Pages project templates provide an out-of-the-box solution for bundling and minification consisting of a JSON configuration file. Third-party tools, such as the [Gulp](xref:client-side/using-gulp) and [Grunt](xref:client-side/using-grunt) task runners, accomplish the same tasks with a bit more complexity. A third-party tool is a great fit when your development workflow requires processing beyond bundling and minification—such as linting and image optimization. By using design-time bundling and minification, the minified files are created prior to the app's deployment. Bundling and minifying before deployment provides the advantage of reduced server load. However, it's important to recognize that design-time bundling and minification increases build complexity and only works with static files.
The MVC and Razor Pages project templates provide a *bundleconfig.json* configuration file which defines the options for each bundle. By default, a single bundle configuration is defined for the custom JavaScript (*wwwroot/js/site.js*) and stylesheet (*wwwroot/css/site.css*) files:
*`outputFileName`: The name of the bundle file to output. Can contain a relative path from the *bundleconfig.json* file. **required**
*`inputFiles`: An array of files to bundle together. These are relative paths to the configuration file. **optional**, *an empty value results in an empty output file. [globbing](http://www.tldp.org/LDP/abs/html/globbingref.html) patterns are supported.
*`minify`: The minification options for the output type. **optional**, *default - `minify: { enabled: true }`*
The [BuildBundlerMinifier](https://www.nuget.org/packages/BuildBundlerMinifier/) NuGet package enables the execution of bundling and minification at build time. The package injects [MSBuild Targets](/visualstudio/msbuild/msbuild-targets) which run at build and clean time. The *bundleconfig.json* file is analyzed by the build process to produce the output files based on the defined configuration.
> BuildBundlerMinifier belongs to a community-driven project on GitHub for which Microsoft provides no support. Issues should be filed [here](https://github.com/madskristensen/BundlerMinifier/issues).
Microsoft (R) Build Engine version 15.4.8.50001 for .NET Core
Copyright (C) Microsoft Corporation. All rights reserved.
Bundler: Cleaning output from bundleconfig.json
Bundler: Done cleaning output file from bundleconfig.json
```
---
## Ad hoc execution of bundling and minification
It's possible to run the bundling and minification tasks on an ad hoc basis, without building the project. Add the [BundlerMinifier.Core](https://www.nuget.org/packages/BundlerMinifier.Core/) NuGet package to your project:
> BundlerMinifier.Core belongs to a community-driven project on GitHub for which Microsoft provides no support. Issues should be filed [here](https://github.com/madskristensen/BundlerMinifier/issues).
This package extends the .NET Core CLI to include the *dotnet-bundle* tool. The following command can be executed in the Package Manager Console (PMC) window or in a command shell:
> NuGet Package Manager adds dependencies to the *.csproj file as `<PackageReference />` nodes. The `dotnet bundle` command is registered with the .NET Core CLI only when a `<DotNetCliToolReference />` node is used. Modify the *.csproj file accordingly.
As a best practice, the bundled and minified files of your app should be used in a production environment. During development, the original files make for easier debugging of the app.
Specify which files to include in your pages by using the [Environment Tag Helper](xref:mvc/views/tag-helpers/builtin-th/environment-tag-helper) in your views. The Environment Tag Helper only renders its contents when running in specific [environments](xref:fundamentals/environments).
The following `environment` tag renders the bundled and minified CSS files when running in an environment other than `Development`. For example, running in `Production` or `Staging` triggers the rendering of these stylesheets:
There are cases in which an app's bundling and minification workflow requires additional processing. Examples include image optimization, cache busting, and CDN asset processing. To satisfy these requirements, you can convert the bundling and minification workflow to use Gulp.
### Use the Bundler & Minifier extension
The Visual Studio [Bundler & Minifier](https://marketplace.visualstudio.com/items?itemName=MadsKristensen.BundlerMinifier) extension handles the conversion to Gulp.
> The Bundler & Minifier extension belongs to a community-driven project on GitHub for which Microsoft provides no support. Issues should be filed [here](https://github.com/madskristensen/BundlerMinifier/issues).
Right-click the *bundleconfig.json* file in Solution Explorer and select **Bundler & Minifier** > **Convert To Gulp...**:
The *gulpfile.js* and *package.json* files are added to the project. The supporting [npm](https://www.npmjs.com/) packages listed in the *package.json* file's `devDependencies` section are installed.
Run the following command in the PMC window to install the Gulp CLI as a global dependency:
```console
npm i -g gulp-cli
```
The *gulpfile.js* file reads the *bundleconfig.json* file for the inputs, outputs, and settings.
To trigger the Gulp minification task before the project builds in Visual Studio, add the following [MSBuild Target](/visualstudio/msbuild/msbuild-targets) to the *.csproj file:
In this example, any tasks defined within the `MyPreCompileTarget` target run before the predefined `Build` target. Output similar to the following appears in Visual Studio's Output window:
```console
1>------ Build started: Project: BuildBundlerMinifierApp, Configuration: Debug Any CPU ------
Alternatively, Visual Studio's Task Runner Explorer may be used to bind Gulp tasks to specific Visual Studio events. See [Running default tasks](xref:client-side/using-gulp#running-default-tasks) for instructions on doing that.
