Fixes that TOC hasn't id attribute when the title is all 2-byte characters (#2994)

* Fix: 2-byte character support of slug

* Fix: Decodes slug to display slug

* Fix: Removed a logic of replaceDiacritics

* Fix: Fixed slugify to pass tests

* Fix: Fixed not to remove underscore

* Adds the test for slugify.js

* Fix: Fix to jump to heading

* Added a comment

* Fix: Created click event only linking to heading

* Fix: Fix to use handleLinkClick(e)

* Fix: Changed the regex rule

* Fix: Changed the regex rule of extractId

tests/lib/slugify-test.js

@@ -0,0 +1,58 @@
+import test from 'ava'
+import slugify from 'browser/lib/slugify'
+
+test('alphabet and digit', t => {
+  const upperAlphabet = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ'
+  const lowerAlphabet = 'abcdefghijklmnopqrstuvwxyz'
+  const digit = '0123456789'
+  const testCase = upperAlphabet + lowerAlphabet + digit
+  const decodeSlug = decodeURI(slugify(testCase))
+
+  t.true(decodeSlug === testCase)
+})
+
+test('should delete unavailable symbols', t => {
+  const availableSymbols = '_-'
+  const testCase = availableSymbols + '][!\'#$%&()*+,./:;<=>?@\\^{|}~`'
+  const decodeSlug = decodeURI(slugify(testCase))
+
+  t.true(decodeSlug === availableSymbols)
+})
+
+test('should convert from white spaces between words to hyphens', t => {
+  const testCase = 'This is one'
+  const expectedString = 'This-is-one'
+  const decodeSlug = decodeURI(slugify(testCase))
+
+  t.true(decodeSlug === expectedString)
+})
+
+test('should remove leading white spaces', t => {
+  const testCase = '                   This is one'
+  const expectedString = 'This-is-one'
+  const decodeSlug = decodeURI(slugify(testCase))
+
+  t.true(decodeSlug === expectedString)
+})
+
+test('should remove trailing white spaces', t => {
+  const testCase = 'This is one                   '
+  const expectedString = 'This-is-one'
+  const decodeSlug = decodeURI(slugify(testCase))
+
+  t.true(decodeSlug === expectedString)
+})
+
+test('2-byte charactor support', t => {
+  const testCase = '菠萝芒果テストÀžƁƵ'
+  const decodeSlug = decodeURI(slugify(testCase))
+
+  t.true(decodeSlug === testCase)
+})
+
+test('emoji', t => {
+  const testCase = '🌸'
+  const decodeSlug = decodeURI(slugify(testCase))
+
+  t.true(decodeSlug === testCase)
+})