True in general, but they use quite a few tricks to minimize the consequences.
They use interpreter, or very unoptimal but fast version of JIT compiler, first time a function is called. They replace it with faster version once it’s clear the function is called a lot.
Unlike C compilers, they don’t need to do that analysis globally for the whole program. They only need to do that for the hot paths, that’s often a small portion of the code.
They can offload that analysis and code generation to another CPU core, and replace the implementation once that background thread has produced a faster version.
