Use C/C to implement Node.js modules (2)_node.js

Reviewing the past and learning the new can make you happy

First of all, please remember this V8 online manual - http://izs.me/v8-docs/main.html.

Do you still remember the building.gyp file from last time?

Copy code The code is as follows:

{
"targets": [
{
"target_name": "addon",
"sources": [ "addon.cc" ]
}
]
}

Just like this, if you have a few more *.cc files, it will look like this:
"sources": [ "addon.cc", "myexample.cc" ]

Last time we separated the two steps. In fact, configuration and compilation can be put together:
$ node-gyp configure build

Have you finished reviewing? without? !

Okay, let’s continue.

Table of Contents

Function parameters

Now we finally have to talk about parameters.

Let us imagine that there is such a function add(a, b) which represents adding a and b and returning the result, so first write the function outline:

Copy code The code is as follows:

#include
using namespace v8;

Handle Add(const Arguments& args)
{
HandleScope scope;

//... Here we go again!
}

Arguments

This is the parameter of the function. Let’s take a look at v8’s official manual reference first.
•int Length() const
•Local operator[](int i) const

We don’t care about the rest, these two are important! One represents the number of parameters passed into the function, and the other bracket is used to access the nth parameter through the subscript index.

Therefore, we can roughly understand the above requirements as args.Length() is 2, args[0] represents a and args[1] represents b. And we need to determine that the type of these two numbers must be Number.

Notice that the index operator in square brackets returns a Local, which is the base class of all types in Node.js. Therefore, the parameters passed in are of uncertain type, and we must determine by ourselves what parameters they are. This is related to some functions of this Value type.

•IsArray()
•IsBoolean()
•IsDate()
•IsFunction()
•IsInt32()
•IsNativeError()
•IsNull()
•IsNumber()
•IsRegExp()
•IsString()
•...

I won’t list them one by one, you can read the documentation for the rest. ｡:.ﾟヽ(*´∀`)ﾉﾟ.:｡

ThrowException

This is a function we will use later. Details can be found in the v8 documentation.

As the name suggests, it throws an error. After executing this statement, it is equivalent to executing a throw() statement in the Node.js local file. For example:
ThrowException(Exception::TypeError(String::New("Wrong number of arguments")));

It is equivalent to executing a Node.js:
throw new TypeError("Wrong number of arguments");

Undefined()

This function is also in the documentation.

Specifically, it is a null value, because some functions do not need to return any specific value, or there is no return value. At this time, Undefined() needs to be used instead.

Let’s do it, Saonian!

After understanding the above points, I believe you will be able to write the logic of a b soon. I will copy the code from the Node.js official manual and give it to you to go through:

Copy code The code is as follows:

#include
using namespace v8;

Handle Add(const Arguments& args)
{
HandleScope scope;

// means that more than 2 parameters can be passed in, but in fact we only use the first two
If(args.Length() < 2)
{
​​​​ // throw error
         ThrowException(Exception::TypeError(String::New("Wrong number of arguments")));

                                                                        // Return null value           return scope.Close(Undefined());
}

// If one of the first two parameters is not a number

If(!args[0]->IsNumber() || !args[1]->IsNumber())
{
                 // Throw an error and return null value
         ThrowException(Exception::TypeError(String::New("Wrong arguments")));
          return scope.Close(Undefined());
}

// Please refer to v8 documentation for details

//
http://izs.me/v8-docs/classv8_1_1Value.html#a6eac2b07dced58f1761bbfd53bf0e366) // `NumberValue` function
Local num = Number::New(args[0]->NumberValue() args[1]->NumberValue());

return scope.Close(num);

}

The function is done!

Finally, write the export function at the end and it’s OK.

Copy code The code is as follows:

void Init(Handle