The Spanish expression 'jaja' comes directly from 'ha', which is the onomatopoeia (sound representation) of laughter in Spanish. While English speakers typically write 'haha' to represent laughter, Spanish speakers double the 'ja' sound instead. This is because in Spanish, the letter 'j' makes a sound similar to the English 'h', and 'a' represents the same vowel sound in both languages.

The Spanish interjection 'ja' (single instance) is related, being the basic unit of this laughter representation. You might also encounter variations like 'jejeje' (representing a softer or more mischievous laugh) and 'jojojo' (often associated with Santa Claus's laugh in Spanish-speaking countries).

While not strictly etymologically related, the English equivalent 'haha' serves the same function and likely arose from a similar onomatopoeic origin. Both 'jaja' and 'haha' are written representations of the universal human sound of laughter, just adapted to the spelling conventions of their respective languages.