The line breaks haven’t worked, here’s it formatted correctly:

Explanation: it’s mostly due to how js does type conversion.

For the Ls, it’s:

• [] is an empty array
• ![] is treated as false
• combining a boolean with the empty array returns “false” as a string (so true + [] = “true”, false + [] = “false”)
• ! + [] is treated as true
• ! + [] + ! + [] is treated as 2 since true + true = 1 + 1 = 2
• so you have “false”[2], which is l

for the o it’s:

• [] is an empty array
• [] + {} returns “[object Object]” as a string ({} + [] returns 0)
• ![] is false
• !![] is true
• +!![] casts it to an integer
• so that part is “[object Object]”[1], which returns “o”-

Iirc this is called “JSFuck”, and it has a number of compilers

There’s a nice presentation that explains this behaviour quite understandable: https://youtu.be/sRWE5tnaxlI