__LINE__ returns the line of code its on, and % 10 means “remainder 10.” Examples:

1 % 10 == 1
...
8 % 10 == 8
9 % 10 == 9
10 % 10 == 0 <-- loops back to 0
11 % 10 == 1
12 % 10 == 2
...
19 % 10 == 9
20 % 10 == 0
21 % 10 == 1

In code, 0 means false and 1 (and 2, 3, 4, …) means true.

So, if on line 10, you say:

int dont_delete_database = true;

then it will expand to:

int dont_delete_database = ( 10 % 10 );
// 10 % 10 == 0 which means false
// database dies...

if you add a line before it, so that the code moves to line 11, then suddenly it works:

// THIS COMMENT PREVENTS DATABASE FROM DYING
int dont_delete_database = ( 11 % 10 );
// 11 % 10 == 1, which means true

I’m not really involved in javascript land so im parroting off of what i’ve heard for “why js over ts?”

• it reduces file size since you no longer need to ship source maps
• ctrl+clicking stuff will take you to the definition rather than an unhelpful type declaration
• if you spot a bug in the library, you can edit the source directly than having to recompile/reimport
• ts adds some unnecessary type “gymnastics” (can’t speak for what this means), when all they really want is intellisense thru jsdoc

So mainly: devs who don’t prefer strongly typed languages, and library devs who find typescript to be less transparent and more time consuming for new and old contributors than it’s worth