High performance is hard, and it depends on many factors. Best performance should be a constant goal for developers. To achieve it, a developer must know the programming language they use and, more importantly, how the language performs under heavy loads, these being disk, memory, network, and processor usage.
Developers will make the most out of a language if they know its weaknesses. In a perfect world, since every job is different, a developer should look for the best tool for the job. But this is not feasible and a developer wouldn't be able to know every best tool, so they have to look for the second best tool for every job. A developer will excel if they know few tools but master them.
As a metaphor, a hammer is used to drive nails, and you can also use it to break objects apart or forge metals, but you shouldn't use it to drive screws. The same applies to languages and platforms. Some platforms are very good for a lot of jobs but perform really badly at other jobs. This performance can sometimes be mitigated, but at other times, can't be avoided and you should look for better tools.
Node.js is not a language; it's actually a platform built on top of V8, Google's open source JavaScript engine. This engine implements ECMAScript, which itself is a simple and very flexible language. I say "simple" because it has no way of accessing the network, accessing the disk, or talking to other processes. It can't even stop execution since it has no kind of exit instruction. This language needs some kind of interface model on top of it to be useful. Node.js does this by exposing a (preferably) nonblocking I/O model using libuv. This nonblocking API allows you to access the filesystem, connect to network services and execute child processes.
The API also has two other important elements: buffers and streams. Since JavaScript strings are Unicode friendly, buffers were introduced to help deal with binary data. Streams are used as simple event interfaces to pass data around. Buffers and streams are used all over the API when reading file contents or receiving network packets.
A stream is a module, similar to the network module. When loaded, it provides access to some base classes that help create readable, writable, duplex, and transform streams. These can be used to perform all sorts of data manipulation in a simplified and unified format.
The buffers module easily becomes your best friend when converting binary data formats to some other format, for example, JSON. Multiple read and write methods help you convert integers and floats, signed or not, big endian or little endian, from 8 bits to 8 bytes long.
Most of the platform is designed to be simple, small, and stable. It's designed and ready to create some high-performance applications.