# Bower {#sec-bower} [Bower](https://bower.io) is a package manager for web site front-end components. Bower packages (comprising of build artefacts and sometimes sources) are stored in `git` repositories, typically on Github. The package registry is run by the Bower team with package metadata coming from the `bower.json` file within each package. The end result of running Bower is a `bower_components` directory which can be included in the web app's build process. Bower can be run interactively, by installing `nodePackages.bower`. More interestingly, the Bower components can be declared in a Nix derivation, with the help of `nodePackages.bower2nix`. ## bower2nix usage {#ssec-bower2nix-usage} Suppose you have a `bower.json` with the following contents: ### Example bower.json {#ex-bowerJson} ```json "name": "my-web-app", "dependencies": { "angular": "~1.5.0", "bootstrap": "~3.3.6" } ``` Running `bower2nix` will produce something like the following output: ```nix { fetchbower, buildEnv }: buildEnv { name = "bower-env"; ignoreCollisions = true; paths = [ (fetchbower "angular" "1.5.3" "~1.5.0" "1749xb0firxdra4rzadm4q9x90v6pzkbd7xmcyjk6qfza09ykk9y") (fetchbower "bootstrap" "3.3.6" "~3.3.6" "1vvqlpbfcy0k5pncfjaiskj3y6scwifxygfqnw393sjfxiviwmbv") (fetchbower "jquery" "2.2.2" "1.9.1 - 2" "10sp5h98sqwk90y4k6hbdviwqzvzwqf47r3r51pakch5ii2y7js1") ]; ``` Using the `bower2nix` command line arguments, the output can be redirected to a file. A name like `bower-packages.nix` would be fine. The resulting derivation is a union of all the downloaded Bower packages (and their dependencies). To use it, they still need to be linked together by Bower, which is where `buildBowerComponents` is useful. ## buildBowerComponents function {#ssec-build-bower-components} The function is implemented in [pkgs/development/bower-modules/generic/default.nix](https://github.com/NixOS/nixpkgs/blob/master/pkgs/development/bower-modules/generic/default.nix). ### Example buildBowerComponents {#ex-buildBowerComponents} ```{=docbook} <programlisting language="nix"> bowerComponents = buildBowerComponents { name = "my-web-app"; generated = ./bower-packages.nix; <co xml:id="ex-buildBowerComponents-1" /> src = myWebApp; <co xml:id="ex-buildBowerComponents-2" /> }; </programlisting> ``` In ["buildBowerComponents" example](#ex-buildBowerComponents) the following arguments are of special significance to the function: ```{=docbook} <calloutlist> <callout arearefs="ex-buildBowerComponents-1"> <para> <varname>generated</varname> specifies the file which was created by <command>bower2nix</command>. </para> </callout> <callout arearefs="ex-buildBowerComponents-2"> <para> <varname>src</varname> is your project's sources. It needs to contain a <filename>bower.json</filename> file. </para> </callout> </calloutlist> ``` `buildBowerComponents` will run Bower to link together the output of `bower2nix`, resulting in a `bower_components` directory which can be used. Here is an example of a web frontend build process using `gulp`. You might use `grunt`, or anything else. ### Example build script (gulpfile.js) {#ex-bowerGulpFile} ```javascript var gulp = require('gulp'); gulp.task('default', [], function () { gulp.start('build'); }); gulp.task('build', [], function () { console.log("Just a dummy gulp build"); gulp .src(["./bower_components/**/*"]) .pipe(gulp.dest("./gulpdist/")); }); ``` ### Example Full example — default.nix {#ex-buildBowerComponentsDefaultNix} ```{=docbook} <programlisting language="nix"> { myWebApp ? { outPath = ./.; name = "myWebApp"; } , pkgs ? import <nixpkgs> {} }: pkgs.stdenv.mkDerivation { name = "my-web-app-frontend"; src = myWebApp; buildInputs = [ pkgs.nodePackages.gulp ]; bowerComponents = pkgs.buildBowerComponents { <co xml:id="ex-buildBowerComponentsDefault-1" /> name = "my-web-app"; generated = ./bower-packages.nix; src = myWebApp; }; buildPhase = '' cp --reflink=auto --no-preserve=mode -R $bowerComponents/bower_components . <co xml:id="ex-buildBowerComponentsDefault-2" /> export HOME=$PWD <co xml:id="ex-buildBowerComponentsDefault-3" /> ${pkgs.nodePackages.gulp}/bin/gulp build <co xml:id="ex-buildBowerComponentsDefault-4" /> ''; installPhase = "mv gulpdist $out"; } </programlisting> ``` A few notes about [Full example — `default.nix`](#ex-buildBowerComponentsDefaultNix): ```{=docbook} <calloutlist> <callout arearefs="ex-buildBowerComponentsDefault-1"> <para> The result of <varname>buildBowerComponents</varname> is an input to the frontend build. </para> </callout> <callout arearefs="ex-buildBowerComponentsDefault-2"> <para> Whether to symlink or copy the <filename>bower_components</filename> directory depends on the build tool in use. In this case a copy is used to avoid <command>gulp</command> silliness with permissions. </para> </callout> <callout arearefs="ex-buildBowerComponentsDefault-3"> <para> <command>gulp</command> requires <varname>HOME</varname> to refer to a writeable directory. </para> </callout> <callout arearefs="ex-buildBowerComponentsDefault-4"> <para> The actual build command. Other tools could be used. </para> </callout> </calloutlist> ``` ## Troubleshooting {#ssec-bower2nix-troubleshooting} ### ENOCACHE errors from buildBowerComponents This means that Bower was looking for a package version which doesn't exist in the generated `bower-packages.nix`. If `bower.json` has been updated, then run `bower2nix` again. It could also be a bug in `bower2nix` or `fetchbower`. If possible, try reformulating the version specification in `bower.json`.