numpy-like package for node

Here is Google's TensorFlow.js (previously https://deeplearnjs.org), which does exactly that, and has built in capacities to train deep neural networks on GPUs using WebGL. You can also port TensorFlow models to it.

Don't be fooled into thinking this is only for deep learning. It is a fully fledged numerical computing platform with built-in GPU acceleration. It follows the eager "execute as you go" model, like NumPy (and Tensorflow Eager, and PyTorch, and others), not the "define then run" model like Tensorflow. As such, it will feel natural to use to anyone who has used NumPy before.

Here is the very informative Github repo:

https://github.com/tensorflow/tfjs-core (the old link https://github.com/PAIR-code/deeplearnjs now redirects there)

No, there are no technical reasons why a numpy-like package does not exist for Node.js and, more generally, JavaScript.

There are two main obstacles preventing Node.js and JavaScript from achieving more mind share in the data science and numeric computing communities.

The first obstacle is community. While the JavaScript community is huge, the subset of people within that community doing interesting things in numeric computing is small. Hence, if you want to do numeric computing in JavaScript and Node.js, finding resources to help you along the way can be hard, and it may feel like a lonely endeavor.

Next, the absence of comparable libraries (chicken and egg: libraries are needed to attract library authors and authors are needed to write good libraries). There are no technical reasons why libraries cannot be written in JavaScript or leverage Node.js (e.g., via native add-ons). I know, as I have written many numeric computing libraries in JavaScript. So while numeric computing is possible in JavaScript, the problem stems from an inability to attract developers having sufficient expertise and capable of putting in the time and effort needed to write high quality numeric computing implementations.

Regarding the specific language features mentioned in the OP:

• ES6/ES2015: none of the recent language additions help or hinder development of numeric computing libraries in JavaScript. Potential additions like list comprehensions will not be game changers either. The one change to the web platform which will make a difference is WebAssembly. With WebAssembly, compiling C/C++/Fortran libraries to run in web browsers will be made easier. At the time of this answer, WebAssembly looks to be the means for bringing SIMD to the web, potentially allowing some speed-ups, although the focus seems to be on short SIMD, rather than long. But even with WebAssembly, porting numeric computing libraries to the web will not be as simple as hitting the compile button. Numeric computing code bases will need to massaged to become amenable for use on the web, and, even then, higher level APIs will likely need to be written to mask some of lower level features, such as manually managing the heap.
• Native add-ons: yes, node modules can be written as native add-ons, allowing C/C++/Fortran code to be used within a Node.js application. Individuals have written libraries to this end; for example, see stdlib. If done well, Node.js can perform numeric computations at speeds comparable to directly using native implementations.
• Typed arrays: as they are now, they are suitable for numeric computation. Similar to C, you can create pooled buffers, which allow for efficient memory reuse and better performance. Furthermore, similar to languages like R, Python, and Julia, you can leverage typed arrays to create ndarray (aka strided array) interfaces. While U/Int64 integer arrays are not currently available at the time of this answer, (a) their absence is not a show stopper and (b) proposals are advancing at the specification level to add U/Int64 integer arrays to JavaScript. Ditto for complex numbers with structured types.

My personal belief is that some form of numeric computing is inevitable in JavaScript and Node.js. The advantages (ubiquity, distribution, performance) and potential applications (edge computing, integrating machine learning, data visualization) are too strong of evolutionary forces not to support data science applications, at least at a basic level.

disclosure: I and others are currently working on a project (https://github.com/stdlib-js/stdlib) which aims to provide numeric computing facilities in JavaScript and Node.js.