I don't agree with his overall thought process, but JavaScript is not without issues. I believe what he's referring to here is that JS will (usually) determine its actions based on its runtime type whereas C will (usually) determine its action based on the compile time type. So if I am expecting a number but get passed a string, in JS I am now executing string operations (with all operators) whereas in C I'm going to be doing arithmetic as expected but on incorrect data (probably the address of the string). Both of these are likely not be what we want, but the JS can end up with extremely unexpected outcomes, especially if we end up with object mismatches, where as the C is restricted to outcomes for different numeric inputs.

> You receive some JSON over the wire, it's not the right format, and everything blows up in your face.

If I was using a staticly typed JSON parser, like say Rust's or Crystal's, then it would blow up, right there. It'd throw an exception, or pass back a failure value that I have to handle.

JS doesn't do that. It just keeps going, and due to the way it implicitly handles types, getting a list instead of an object can mean you end up with a string later on.

You are right.

I guess that, often, people just JSON.parse and think that's enough 'cause they already typed their stuff. But that's not really a problem of TS or JS.