"Dynamically typed languages such as JavaScript present a challenge to just-in-time compilers. In contrast to statically typed languages such as JVML, in which there are specific opcodes for common operations on primitive types [..], all operations in dynamically typed language such as JavaScript are late-bound. [..] We present a new approach to compiling dynamically typed languages in which code traces observed during execution are dynamically specialized for each actually observed run-time type. For most benchmark programs, our prototype JavaScript virtual machine outperforms every other JavaScript platform known to us."