autorem
A postcss
-dependent node module that converts all px
units in your CSS to rem
units.
Overview
For greater accessibility, it is becoming increasingly important to abandon absolute units like px
in favor of more flexible reference units such as rem
or em
. Since em
is context-dependent, rem
units are much more convenient because they relate to the document's default font-size
(typically 16px
.)
This plugin borrows heavily in terms of design from the node-pixrem
project by @iamvdo.
Usage
Using autorem
is quite simple. Add it to your package.json
file, or just install it in your project directory using npm
like so:
npm install autorem
Once you've done that, you can use it in your node application with the following pattern:
"use strict";
var fs = require("fs");
var autorem = require("autorem");
var css = fs.readFileSync("./example.css", "utf8");
var processedCss = autorem.process(css);
fs.writeFile("example.processed.css", processedCss, function(err){
if(err){
throw err;
}
});
This assumes you have example.css
running in the same folder as this code snippet. The autorem.process
function call also accepts a second argument for some useful options (listed further on in this readme.)
If you like task runners, then you probably want to use something like grunt. Here's a simple Gruntfile.js
example that utilizes grunt-contrib-watch
to watch a CSS file for changes and employs postcss
and autorem
to process any px
values found.
module.exports = function(grunt){
grunt.loadNpmTasks("grunt-contrib-watch");
grunt.loadNpmTasks("grunt-postcss");
// Task Configuration
var taskConfig = {
pkg: grunt.file.readJSON("package.json"),
watch: {
options: {
livereload: true,
livereloadOnError: false,
reload: true
},
files: ["css/styles.css"],
tasks: ["postcss:dist"]
},
postcss: {
options: {
processors: [
require("autorem")({
// Options
legacy: true
})
]
},
dist: {
src: "css/styles.processed.css"
}
}
};
grunt.initConfig(taskConfig);
grunt.registerTask("default", ["postcss:dist", "watch"]);
};
It will then transform your css from something like this:
p
{
font-size: 24px;
padding: 16px 32px;
margin: 0 0 16px 0;
}
Into something like this:
p
{
font-size: 1.5rem;
padding: 1rem 2rem;
margin: 0 0 1rem 0;
}
Options
baseFontSize
default: 16
All browser user agent stylesheets set a default font-size
property of 16px
. autorem
mimics this with a default of 16
, which you should preserve for new projects. You can override this with your own numeric value if necessary.
legacy
default: false
By default autorem
will simply replace all of your rules with px
units with their respective rem
values. Older browsers have issues with rem
units. If you want to provide fallback support to those browsers, set this value to true and autorem
will preserve your rules with px
and append a duplicate rule with the rem
equivalent.
skipMediaQueries
default: false
autorem
will process pixel values in media queries by default. If you don't like that, you can flip this to true
.
Known Limitations
autorem
does not allow you to specify more than one base value. Some folks may prefer to set a font-size
property on the <html>
or <body>
elements per breakpoint. autorem
will steamroll this and use a single reference of 16px
to calculate rem
values regardless of the breakpoint's default. I don't plan on fixing this. Use JavaScript or CSS classes to programmatically change your user's viewing experience for the moment. I'm not necessarily convinced that's a bad practice, and having a consistent default is preferable in most projects I have worked on.
Issues
I'm not aware of any, but some may exist. If you run into problems with autorem
, log a bug. Or submit a pull request and fix it, and I'll incorporate it.
Special Thanks
Thanks to @iamvdo for his pixrem
node module, from which autorem
draws much of its inspiration and design.