Use ESM

.gitignore

@@ -1,6 +1,5 @@
-.DS_Store
-*.log
-.nyc_output/
 coverage/
 node_modules/
+.DS_Store
+*.log
 yarn.lock

.prettierignore

@@ -1,3 +1,2 @@
 coverage/
-*.json
 *.md

index.js

@@ -1,2 +1,156 @@
-exports.fromMarkdown = require('./from-markdown.js')
-exports.toMarkdown = require('./to-markdown.js')
+import repeat from 'repeat-string'
+import {longestStreak} from 'longest-streak'
+import safe from 'mdast-util-to-markdown/lib/util/safe.js'
+
+export const mathFromMarkdown = {
+  enter: {
+    mathFlow: enterMathFlow,
+    mathFlowFenceMeta: enterMathFlowMeta,
+    mathText: enterMathText
+  },
+  exit: {
+    mathFlow: exitMathFlow,
+    mathFlowFence: exitMathFlowFence,
+    mathFlowFenceMeta: exitMathFlowMeta,
+    mathFlowValue: exitMathData,
+    mathText: exitMathText,
+    mathTextData: exitMathData
+  }
+}
+
+export const mathToMarkdown = {
+  unsafe: [
+    {character: '\r', inConstruct: ['mathFlowMeta']},
+    {character: '\r', inConstruct: ['mathFlowMeta']},
+    {character: '$', inConstruct: ['mathFlowMeta', 'phrasing']},
+    {atBreak: true, character: '$', after: '\\$'}
+  ],
+  handlers: {math, inlineMath}
+}
+
+inlineMath.peek = inlineMathPeek
+
+function enterMathFlow(token) {
+  this.enter(
+    {
+      type: 'math',
+      meta: null,
+      value: '',
+      data: {
+        hName: 'div',
+        hProperties: {className: ['math', 'math-display']},
+        hChildren: [{type: 'text', value: ''}]
+      }
+    },
+    token
+  )
+}
+
+function enterMathFlowMeta() {
+  this.buffer()
+}
+
+function exitMathFlowMeta() {
+  var data = this.resume()
+  this.stack[this.stack.length - 1].meta = data
+}
+
+function exitMathFlowFence() {
+  // Exit if this is the closing fence.
+  if (this.getData('mathFlowInside')) return
+  this.buffer()
+  this.setData('mathFlowInside', true)
+}
+
+function exitMathFlow(token) {
+  var data = this.resume().replace(/^(\r?\n|\r)|(\r?\n|\r)$/g, '')
+  var node = this.exit(token)
+  node.value = data
+  node.data.hChildren[0].value = data
+  this.setData('mathFlowInside')
+}
+
+function enterMathText(token) {
+  this.enter(
+    {
+      type: 'inlineMath',
+      value: '',
+      data: {
+        hName: 'span',
+        hProperties: {className: ['math', 'math-inline']},
+        hChildren: [{type: 'text', value: ''}]
+      }
+    },
+    token
+  )
+  this.buffer()
+}
+
+function exitMathText(token) {
+  var data = this.resume()
+  var node = this.exit(token)
+  node.value = data
+  node.data.hChildren[0].value = data
+}
+
+function exitMathData(token) {
+  this.config.enter.data.call(this, token)
+  this.config.exit.data.call(this, token)
+}
+
+function math(node, _, context) {
+  var raw = node.value || ''
+  var fence = repeat('$', Math.max(longestStreak(raw, '$') + 1, 2))
+  var exit = context.enter('mathFlow')
+  var value = fence
+  var subexit
+
+  if (node.meta) {
+    subexit = context.enter('mathFlowMeta')
+    value += safe(context, node.meta, {before: '$', after: ' ', encode: ['$']})
+    subexit()
+  }
+
+  value += '\n'
+
+  if (raw) {
+    value += raw + '\n'
+  }
+
+  value += fence
+  exit()
+  return value
+}
+
+function inlineMath(node) {
+  var value = node.value || ''
+  var size = 1
+  var pad = ''
+  var sequence
+
+  // If there is a single dollar sign on its own in the math, use a fence of
+  // two.
+  // If there are two in a row, use one.
+  while (
+    new RegExp('(^|[^$])' + repeat('\\$', size) + '([^$]|$)').test(value)
+  ) {
+    size++
+  }
+
+  // If this is not just spaces or eols (tabs don’t count), and either the first
+  // or last character are a space, eol, or dollar sign, then pad with spaces.
+  if (
+    /[^ \r\n]/.test(value) &&
+    (/[ \r\n$]/.test(value.charAt(0)) ||
+      /[ \r\n$]/.test(value.charAt(value.length - 1)))
+  ) {
+    pad = ' '
+  }
+
+  sequence = repeat('$', size)
+  return sequence + pad + value + pad + sequence
+}
+
+function inlineMathPeek() {
+  return '$'
+}

package.json

@@ -26,38 +26,33 @@
   "contributors": [
     "Titus Wormer <tituswormer@gmail.com> (https://wooorm.com)"
   ],
+  "sideEffects": false,
+  "type": "module",
+  "main": "index.js",
   "files": [
-    "from-markdown.js",
-    "index.js",
-    "to-markdown.js"
+    "index.js"
   ],
   "dependencies": {
-    "longest-streak": "^2.0.0",
+    "longest-streak": "^3.0.0",
     "mdast-util-to-markdown": "^0.6.0",
     "repeat-string": "^1.0.0"
   },
   "devDependencies": {
+    "c8": "^7.0.0",
     "mdast-util-from-markdown": "^0.8.0",
     "micromark-extension-math": "^0.1.0",
-    "nyc": "^15.0.0",
     "prettier": "^2.0.0",
     "remark-cli": "^9.0.0",
     "remark-preset-wooorm": "^8.0.0",
     "tape": "^5.0.0",
-    "xo": "^0.38.0"
+    "xo": "^0.39.0"
   },
   "scripts": {
     "format": "remark . -qfo && prettier . -w --loglevel warn && xo --fix",
-    "test-api": "node test",
-    "test-coverage": "nyc --reporter lcov tape test.js",
+    "test-api": "node --conditions development test.js",
+    "test-coverage": "c8 --check-coverage --branches 100 --functions 100 --lines 100 --statements 100 --reporter lcov node --conditions development test.js",
     "test": "npm run format && npm run test-coverage"
   },
-  "nyc": {
-    "check-coverage": true,
-    "lines": 100,
-    "functions": 100,
-    "branches": 100
-  },
   "prettier": {
     "tabWidth": 2,
     "useTabs": false,
@@ -68,7 +63,10 @@
   },
   "xo": {
     "prettier": true,
-    "esnext": false
+    "rules": {
+      "no-var": "off",
+      "prefer-arrow-callback": "off"
+    }
   },
   "remarkConfig": {
     "plugins": [

readme.md

@@ -18,6 +18,9 @@ You probably shouldn’t use this package directly, but instead use
 
 ## Install
 
+This package is [ESM only](https://gist.github.com/sindresorhus/a39789f98801d908bbc7ff3ecc99d99c):
+Node 12+ is needed to use it and it must be `import`ed instead of `require`d.
+
 [npm][]:
 
 ```sh
@@ -90,13 +93,13 @@ $$
 
 ## API
 
-### `math.fromMarkdown`
+This package exports the following identifier: `mathFromMarkdown`,
+`mathToMarkdown`.
+There is no default export.
 
-### `math.toMarkdown`
+### `mathFromMarkdown`
 
-> Note: the separate extensions are also available at
-> `mdast-util-math/from-markdown` and
-> `mdast-util-math/to-markdown`.
+### `mathToMarkdown`
 
 Support math.
 These exports are extensions, respectively for