MathJax 2 only loads components as needed (to reduce payload size).

• The input and output formats used
• Infrequently accessed parts
  • Unusual TEX commands (e.g., \bbox)
  • Support for linebreaks
  • Little-used output features (e.g., support for <menclose>)
  • TEX extensions on demand (e.g., \require{...})
• Data for fonts as needed (e.g., Fraktur, Sans-Serif)

This makes configuring MathJax 2 very flexible, since it can be done at run time (i.e., in the page).

But its dynamic loader doesn't play well with webpack or other modern packaging strategies.