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doc: copyedit addons doc
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PR-URL: #4185
Reviewed-By: Roman Reiss <[email protected]>
Reviewed-By: Michaël Zasso <[email protected]>
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Trott authored and Myles Borins committed Jan 19, 2016
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# Addons

Addons are dynamically linked shared objects. They can provide glue to C and
Addons are dynamically-linked shared objects. They can provide glue to C and
C++ libraries. The API (at the moment) is rather complex, involving
knowledge of several libraries:

Expand All @@ -11,11 +11,11 @@ knowledge of several libraries:

- [libuv][], C event loop library. Anytime one needs to wait for a file
descriptor to become readable, wait for a timer, or wait for a signal
to be received one will need to interface with libuv. That is, if you
to be received, one will need to interface with libuv. That is, if you
perform any I/O, libuv will need to be used.

- Internal Node.js libraries. Most importantly is the `node::ObjectWrap`
class which you will likely want to derive from.
- Internal Node.js libraries. The most important class is `node::ObjectWrap`
which you will likely want to derive from.

- Others. Look in `deps/` for what else is available.

Expand All @@ -28,7 +28,7 @@ be used as a starting-point for your own Addon.

## Hello world

To get started let's make a small Addon which is the C++ equivalent of
To get started, let's make a small Addon which is the C++ equivalent of
the following JavaScript code:

module.exports.hello = function() { return 'world'; };
Expand Down Expand Up @@ -68,11 +68,11 @@ Note that all Node.js addons must export an initialization function:
There is no semi-colon after `NODE_MODULE` as it's not a function (see
`node.h`).

The `module_name` needs to match the filename of the final binary (minus the
.node suffix).
The `module_name` needs to match the filename of the final binary (excluding
the .node suffix).

The source code needs to be built into `addon.node`, the binary Addon. To
do this we create a file called `binding.gyp` which describes the configuration
do this, we create a file called `binding.gyp` which describes the configuration
to build your module in a JSON-like format. This file gets compiled by
[node-gyp][].

Expand All @@ -89,13 +89,13 @@ The next step is to generate the appropriate project build files for the
current platform. Use `node-gyp configure` for that.

Now you will have either a `Makefile` (on Unix platforms) or a `vcxproj` file
(on Windows) in the `build/` directory. Next invoke the `node-gyp build`
(on Windows) in the `build/` directory. Next, invoke the `node-gyp build`
command.

Now you have your compiled `.node` bindings file! The compiled bindings end up
in `build/Release/`.

You can now use the binary addon in an Node.js project `hello.js` by pointing
You can now use the binary addon in a Node.js project `hello.js` by pointing
`require` to the recently built `hello.node` module:

// hello.js
Expand All @@ -114,7 +114,7 @@ Below are some addon patterns to help you get started. Consult the online
[Embedder's Guide][] for an explanation of several concepts used such as
handles, scopes, function templates, etc.

In order to use these examples you need to compile them using `node-gyp`.
In order to use these examples, you need to compile them using `node-gyp`.
Create the following `binding.gyp` file:

{
Expand All @@ -127,7 +127,7 @@ Create the following `binding.gyp` file:
}

In cases where there is more than one `.cc` file, simply add the file name to
the `sources` array, e.g.:
the `sources` array. For example:

"sources": ["addon.cc", "myexample.cc"]

Expand Down Expand Up @@ -234,7 +234,7 @@ the full `module` object as the second argument. This allows the addon
to completely overwrite `exports` with a single function instead of
adding the function as a property of `exports`.

To test it run the following JavaScript snippet:
To test it, run the following JavaScript snippet:

// test.js
var addon = require('./build/Release/addon');
Expand Down Expand Up @@ -344,8 +344,8 @@ To test:

### Wrapping C++ objects

Here we will create a wrapper for a C++ object/class `MyObject` that can be
instantiated in JavaScript through the `new` operator. First prepare the main
Here, we will create a wrapper for a C++ object/class `MyObject` that can be
instantiated in JavaScript through the `new` operator. First, prepare the main
module `addon.cc`:

// addon.cc
Expand All @@ -365,7 +365,7 @@ module `addon.cc`:

} // namespace demo

Then in `myobject.h` make your wrapper inherit from `node::ObjectWrap`:
Then, in `myobject.h`, make your wrapper inherit from `node::ObjectWrap`:

// myobject.h
#ifndef MYOBJECT_H
Expand Down Expand Up @@ -394,7 +394,7 @@ Then in `myobject.h` make your wrapper inherit from `node::ObjectWrap`:

#endif

And in `myobject.cc` implement the various methods that you want to expose.
And in `myobject.cc`, implement the various methods that you want to expose.
Here we expose the method `plusOne` by adding it to the constructor's
prototype:

Expand Down Expand Up @@ -480,7 +480,8 @@ Test it with:
### Factory of wrapped objects

This is useful when you want to be able to create native objects without
explicitly instantiating them with the `new` operator in JavaScript, e.g.
explicitly instantiating them with the `new` operator in JavaScript. For
example:

var obj = addon.createObject();
// instead of:
Expand Down Expand Up @@ -515,8 +516,9 @@ Let's register our `createObject` method in `addon.cc`:

} // namespace demo

In `myobject.h` we now introduce the static method `NewInstance` that takes
care of instantiating the object (i.e. it does the job of `new` in JavaScript):
In `myobject.h`, we now introduce the static method `NewInstance` that takes
care of instantiating the object. In other words, it does the job of `new` in
JavaScript:

// myobject.h
#ifndef MYOBJECT_H
Expand Down Expand Up @@ -644,9 +646,9 @@ Test it with:
### Passing wrapped objects around

In addition to wrapping and returning C++ objects, you can pass them around
by unwrapping them with Node.js's `node::ObjectWrap::Unwrap` helper function.
In the following `addon.cc` we introduce a function `add()` that can take on two
`MyObject` objects:
by unwrapping them with the Node.js helper function `node::ObjectWrap::Unwrap`.
In the following `addon.cc`, we introduce a function `add()` that can take on
two `MyObject` objects:

// addon.cc
#include <node.h>
Expand Down Expand Up @@ -690,7 +692,7 @@ In the following `addon.cc` we introduce a function `add()` that can take on two

} // namespace demo

To make things interesting we introduce a public method in `myobject.h` so we
To make things interesting, we introduce a public method in `myobject.h` so we
can probe private values after unwrapping the object:

// myobject.h
Expand Down Expand Up @@ -721,7 +723,7 @@ can probe private values after unwrapping the object:

#endif

The implementation of `myobject.cc` is similar as before:
The implementation of `myobject.cc` is similar to before:

// myobject.cc
#include <node.h>
Expand Down Expand Up @@ -804,10 +806,10 @@ Test it with:
* `callback`: `void (*)(void*)` - A pointer to the function to call at exit.
* `args`: `void*` - A pointer to pass to the callback at exit.

Registers exit hooks that run after the event loop has ended, but before the VM
Registers exit hooks that run after the event loop has ended but before the VM
is killed.

Callbacks are run in last-in, first-out order. AtExit takes two parameters:
Callbacks are run in last-in first-out order. AtExit takes two parameters:
a pointer to a callback function to run at exit, and a pointer to untyped
context data to be passed to that callback.

Expand Down

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