Em dashes used as parenthetical dividers, and en dashes when used as word joiners, are usually set continuous with the text. However, such a dash can optionally be surrounded with a hair space, U+200A, or thin space, U+2009 or HTML named entities   and   These spaces are much thinner than a normal space (except in a monospaced (non-proportional) font), with the hair space in particular being the thinnest of horizontal whitespace characters.

https://en.wikipedia.org/wiki/Whitespace_character#Hair_spac...

Typographers usually add space to the left side of the following marks:

    : ; ” ’ ! ? / ) ] } * ¿ › » @ ® ™ ℓ ° ¡ ' " † + = ÷ - – —

    “ ‘ / ( [ { > ≥ < ≤ £ $ ¢ € ‹ « √ μ # @ + = ÷ - – —

1. (letterpress typography) A piece of metal type used to create the narrowest space. 2. (typography, US) The narrowest space appearing between letters and punctuation.

https://en.wiktionary.org/wiki/hair_space

Now I'd like to see how the metal type looks like, but ehm... it's difficult googling it. Also a whole collection of space types and what they're called in other languages.