Add support for passing a function as the prefix

__tests__/applyClassPrefix.test.js

@@ -16,3 +16,27 @@ test('it prefixes classes with the provided prefix', () => {
  expect(result.css).toEqual(expected)
  expect(result.warnings().length).toBe(0)
 })
+
+test('it handles a function as the prefix', () => {
+ const input = postcss.parse(`
+ .foo { color: red; }
+ .apple, .pear { color: green; }
+ `)
+
+ const expected = `
+ .tw-foo { color: red; }
+ .apple, .pear { color: green; }
+ `
+
+ const prefixFunc = selector => {
+ if (selector === '.foo') {
+ return 'tw-'
+ }
+
+ return ''
+ }
+
+ const result = applyClassPrefix(input, prefixFunc).toResult()
+ expect(result.css).toEqual(expected)
+ expect(result.warnings().length).toBe(0)
+})

src/util/applyClassPrefix.js

@@ -1,6 +1,9 @@
 export default function(css, prefix) {
+ const prefixIsFunc = typeof prefix === 'function'
  css.walkRules(rule => {
- rule.selectors = rule.selectors.map(selector => `.${prefix}${selector.slice(1)}`)
+ rule.selectors = rule.selectors.map(
+ selector => `.${prefixIsFunc ? prefix(selector) : prefix}${selector.slice(1)}`
+ )
  })
  return css
 }