Build Table of Contents dynamically in pure JS

With some stuffs

And foo bar

Test 2

aaaaa

Test 2.1

Test 2.2

Test 2.3

Test 3

Test 3.1

Test 3.2

Test 3.3

Test 3.3.1

Test 3.3.1.1

Test 3.3.1.2

Test 3.3.1.3

Test 3.3.1.3.1

Test 3.3.2