Add API to convert browserslist to targets

Author: devongovett

README.md

@@ -45,7 +45,9 @@ A CSS parser, transformer, and minifier written in Rust.
 
 ### From JavaScript
 
-More docs to come, but here is a simple example:
+See the [TypeScript definitions](blob/master/node/index.d.ts) for full API docs.
+
+Here is a simple example that compiles the input CSS for Safari 13.2, and minifies the output.
 
 ```js
 const css = require('@parcel/css');
@@ -63,6 +65,15 @@ let {code, map} = css.transform({
 });
 ```
 
+You can also convert the results of running `browserslist` into targets which can be passed to `@parcel/css`:
+
+```js
+const browserslist = require('browserslist');
+const css = require('@parcel/css');
+
+let targets = css.browserslistToTargets(browserslist('>= 0.25%'));
+```
+
 ### From Rust
 
 See the Rust API docs on [docs.rs](https://docs.rs/parcel_css).

bench.js

@@ -1,4 +1,4 @@
-const css = require('./native');
+const css = require('./');
 const cssnano = require('cssnano');
 const postcss = require('postcss');
 const esbuild = require('esbuild');

node/browserslistToTargets.js

@@ -0,0 +1,48 @@
+const BROWSER_MAPPING = {
+  and_chr: 'chrome',
+  and_ff: 'firefox',
+  ie_mob: 'ie',
+  op_mob: 'opera',
+  and_qq: null,
+  and_uc: null,
+  baidu: null,
+  bb: null,
+  kaios: null,
+  op_mini: null,
+};
+
+function browserslistToTargets(browserslist) {
+  let targets = {};
+  for (let browser of browserslist) {
+    let [name, v] = browser.split(' ');
+    if (BROWSER_MAPPING[name] === null) {
+      continue;
+    }
+
+    let version = parseVersion(v);
+    if (version == null) {
+      continue;
+    }
+
+    if (targets[name] == null || version < targets[name]) {
+      targets[name] = version;
+    }
+  }
+
+  return targets;
+}
+
+function parseVersion(version) {
+  let [major, minor = 0, patch = 0] = version
+    .split('-')[0]
+    .split('.')
+    .map(v => parseInt(v, 10));
+
+  if (isNaN(major) || isNaN(minor) || isNaN(patch)) {
+    return null;
+  }
+
+  return (major << 16) | (minor << 8) | patch;
+}
+
+module.exports = browserslistToTargets;

node/index.d.ts

@@ -163,3 +163,9 @@ export interface TransformAttributeResult {
  * Compiles a single CSS declaration list, such as an inline style attribute in HTML.
  */
 export declare function transformStyleAttribute(options: TransformAttributeOptions): TransformAttributeResult;
+
+/**
+ * Converts a browserslist result into targets that can be passed to @parcel/css.
+ * @param browserslist the result of calling `browserslist`
+ */
+export declare function browserslistToTargets(browserslist: string[]): Targets;

native.js node/index.jsnative.js renamed to node/index.js

@@ -14,7 +14,9 @@ if (process.platform === 'linux') {
 
 let name = `parcel-css.${parts.join('-')}.node`;
 if (process.env.CSS_TRANSFORMER_WASM) {
-  module.exports = require(`./pkg`);
+  module.exports = require(`../pkg`);
 } else {
-  module.exports = require(`./${name}`);
+  module.exports = require(`../${name}`);
 }
+
+module.exports.browserslistToTargets = require('./browserslistToTargets');

package.json

@@ -3,7 +3,7 @@
   "version": "1.0.0-alpha.8",
   "license": "MIT",
   "description": "A CSS parser, transformer, and minifier written in Rust",
-  "main": "native.js",
+  "main": "node/index.js",
   "types": "node/index.d.ts",
   "targets": {
     "main": false,
@@ -28,7 +28,8 @@
     "name": "parcel-css"
   },
   "files": [
-    "native.js",
+    "node/*.js",
+    "node/*.d.ts",
     "*.node"
   ],
   "dependencies": {

src/rules/mod.rs

@@ -28,7 +28,7 @@ use crate::vendor_prefix::VendorPrefix;
 use crate::prefixes::Feature;
 use crate::targets::Browsers;
 use std::collections::{HashMap, HashSet};
-use crate::selector::{is_equivalent, get_prefix, get_necessary_prefixes, is_unused};
+use crate::selector::{is_equivalent, get_prefix, get_necessary_prefixes};
 use crate::error::PrinterError;
 use crate::logical::LogicalProperties;