That's my interpretation. Modern JS engines have multiple tiers of optimization, which they apply in different ways based on how "hot" a piece of JavaScript is.

That's my interpretation. Modern JS engines have multiple tiers of optimization, which they apply in different ways based on how "hot" a piece of JavaScript is. JIT is the highest level of optimization, but also means generating and executing native code on the fly, which I assume leaves the door open for worse exploits if there's a bug in the engine. This is in contrast with bytecode interpretation, which is slower but available.