diff --git a/package.json b/package.json
index 4c67093..a76aaad 100644
--- a/package.json
+++ b/package.json
@@ -18,7 +18,8 @@
     "serve": "rimraf dist && NODE_ENV=development rollup -c --watch",
     "build": "rimraf dist && NODE_ENV=production rollup -c && NODE_ENV=production DISABLE_BABEL=yes rollup -c",
     "test": "jest",
-    "lint": "standard 'src/**'"
+    "lint": "standard 'src/**'",
+    "lint:fix": "standard 'src/**' --fix"
   },
   "main": "dist/maska.umd.js",
   "module": "dist/maska.esm.js",
diff --git a/src/mask.js b/src/mask.js
index 455da03..7c7e38d 100644
--- a/src/mask.js
+++ b/src/mask.js
@@ -69,7 +69,7 @@ function process (value, mask, tokens, masked = true) {
     }
   }
 
-  // fix mask that ends with parentesis
+  // fix mask that ends with parenthesis
   while (masked && im < mask.length) { // eslint-disable-line no-unmodified-loop-condition
     const maskCharRest = mask[im]
     if (tokens[maskCharRest]) {
@@ -83,7 +83,16 @@ function process (value, mask, tokens, masked = true) {
   return ret + rest
 }
 
+/**
+ *
+ * @param {String} value
+ * @param {'uppercase' | 'lowercase' | 'transform'} token
+ */
 function tokenTransform (value, token) {
+  if (token.transform) {
+    value = token.transform(value)
+  }
+
   if (token.uppercase) {
     return value.toLocaleUpperCase()
   } else if (token.lowercase) {
diff --git a/src/utils.js b/src/utils.js
index 2e58bf3..99aa322 100644
--- a/src/utils.js
+++ b/src/utils.js
@@ -19,7 +19,7 @@ function fixInputSelection (el, position, digit) {
     position++
   }
 
-  const selectionRange = (el.type && el.type.match(/^(text|search|password|tel|url)$/i) || !el.type)
+  const selectionRange = el.type ? el.type.match(/^(text|search|password|tel|url)$/i) : !el.type
   if (selectionRange && el === document.activeElement) {
     el.setSelectionRange(position, position)
     setTimeout(function () {
@@ -32,4 +32,9 @@ function isString (val) {
   return Object.prototype.toString.call(val) === '[object String]'
 }
 
-export { event, findInputElement, fixInputSelection, isString }
+export {
+  event,
+  findInputElement,
+  fixInputSelection,
+  isString
+}
diff --git a/test/mask.test.js b/test/mask.test.js
index 95573eb..6d8d63a 100644
--- a/test/mask.test.js
+++ b/test/mask.test.js
@@ -120,3 +120,75 @@ test('Dynamic CPF/CNPJ', () => {
     expect(mask('12345678901', '["###.###.###-##", "##.###.###/####-##"]', tokens)).toBe('123.456.789-01')
     expect(mask('12345678901234', '["###.###.###-##", "##.###.###/####-##"]', tokens)).toBe('12.345.678/9012-34')
 })
+
+test('Custom transform: odd number -> 1, even number -> 0', () => {
+    // isOdd
+    const transform = (numberLike) => String(Number(numberLike) % 2)
+
+    expect((mask('1234567890', '#*', {
+        ...tokens,
+        ...{
+            '#': {
+                pattern: /[0-9]/,
+                transform
+            }
+        }
+    }))).toBe('1010101010')
+})
+
+function transliterate(char) {
+    const rule = Object.entries({
+        a: 'а',
+        b: 'в',
+        k: 'к',
+        m: 'м',
+        h: 'н',
+        o: 'о',
+        p: 'р',
+        c: 'с',
+        t: 'т',
+        y: 'у',
+        x: 'х',
+    }).reduce((acc, [from, to]) => {
+        acc[from] = to
+        acc[from.toLocaleUpperCase()] = to.toLocaleUpperCase()
+        return acc
+    }, {})
+    return rule[char]
+}
+
+test('Custom transform: transliterate abkTYX -> авкТУХ', () => {
+    expect(mask('abkTYX', 'T*', {
+        ...tokens,
+        ...{
+            'T': {
+                pattern: /[a-zA-Z]/,
+                transform: transliterate
+            }
+        }
+    })).toBe('авкТУХ')
+})
+
+test('Custom transform with `uppercase` and `lowercase` enabled: abkTYX -> АВКТУХ, abkTYX -> авктух', () => {
+    expect(mask('abkTYX', 'T*', {
+        ...tokens,
+        ...{
+            'T': {
+                pattern: /[a-zA-Z]/,
+                transform: transliterate,
+                uppercase: true,
+            }
+        }
+    })).toBe('АВКТУХ')
+
+    expect(mask('abkTYX', 'T*', {
+        ...tokens,
+        ...{
+            'T': {
+                pattern: /[a-zA-Z]/,
+                transform: transliterate,
+                lowercase: true,
+            }
+        }
+    })).toBe('авктух')
+})
\ No newline at end of file