On Node Modules

Creating a node module is similar to creating a node.js application. We have to run npm init and that’s it!

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A module can be either a single file or a directory containing a set of files. Usually when the module contains more than one file inside a directory it is recommended to have a file named index.js exposed what properties, objects and functions the module provide to outside. However it is not always required to have a file named index.js where we can override this behavior (more on this later).

Importing a module in our application is also straightforward, which can be done using Node’s require function. require function takes the path to a node module as an argument and performs a synchronous look up for the module first in core modules, then the current directory and finally in node_modules. We could omit the .js extension when it comes to requiring. In that case node js will assumes the extension as .js and scan for all JavaScript modules. Since JSON also treated as JavaScript objects, node js will take JSON files in to count when extension is missing. Once the module is located, the require function will return the contents of the exports object defined in the module.

We have two options when it comes to exporting properties or functions; exports and module.exports. exports is a global reference to module.exports and module.exports is what ultimately gets expose to outside. Since exports is a global reference, Node expects it to not be reassigned to any other object. If anything assigned to exports, then the reference between exports and module.exports will be broken.

When it comes to using node modules, Node uses a mechanism to reuse node_modules without knowing their file system location. It search for required node_modules at multiple level.

Finally, Node expects to have a file named index.js in each node module. Otherwise it will scan for a file names package.json inside the module directory and that package.json should contain an element named main specifying the starting point.

Rock on!

On Garbage Collecting C++ Addons in NodeJS

NodeJS Addons are C++ objects that can be loaded into NodeJS using require(). Idea is that this allows NodeJS to gain performance and functionalities of C++. This acts as an interface between JavaScript and C++. NodeJS documentation is helpful to get familiar with Addons>>.

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However, when it comes to garbage collecting (GC), the documentation is missing some important… well I’d refer to those as tricks.

Manually execute GC,

First we have to set the object instance to null and then call the garbage collector in global context.

obj = null;

global.gc();

One consideration with above is that this is not a reliable way to trigger GC on weak handles.

Another approach is to allocated a huge amount of memory so that GC will triggered,

for (let i = 0;  i < 1e6;  ++i) {

({});

}

Also, the GC can be triggered forcefully using V8’s command line flags –gc_global and —gc_interval. –gc_global forces V8 to perform a full garbage collection, while –gc_interval forces V8 to perform garbage collection after a given amount of allocations.

These command line flags are provided by underlying V8 JavaScript engine. They are subjected to change or removal at anytime and not documented by NodeJS or V8. Therefore it is recommended not to use these outside of testing purposes.

References,

Rock on!