#NODEJS

Nodejs is not a language, keep in mind of that. Nodejs is engine like V8 but the difference isNodejsmake Javascript Language run standalone far away browser!

Nodejsis uses V8 engine program which Google created as a part of whole Nodejs's Engine

in first line of codeNodejsprogram you will see this line

#include<include/v8.h>

and this pre-processor directive that grapV8 codeas library into thisC++ program. so that you can call some function/classes that exist inside this library

v8::Local<v8::Value> GetFoo(v8::Local<v8::Context> context,
                            v8::Local<v8::Object> obj) {
  v8::Isolate* isolate = context->GetIsolate();
  v8::EscapableHandleScope handle_scope(isolate);

  // The 'foo_string' handle cannot be returned from this function because
  // it is not “escaped” with `.Escape()`.
  v8::Local<v8::String> foo_string =
      v8::String::NewFromUtf8(isolate, "foo").ToLocalChecked();

  v8::Local<v8::Value> return_value;
  if (obj->Get(context, foo_string).ToLocal(&return_value)) {
    return handle_scope.Escape(return_value);
  } else {
    // There was a JS exception! Handle it somehow.
    return v8::Local<v8::Value>();
  }
}

wherev8is namespace c++ helps you access classes and functions that exist insideV8 engine

like exactly

#include<cmath>

which grap maths functions into your code so that you can call this function for example

pow(5, 2) // 5 * 2 = 10
// this function exist inside <cmath> library

#How to add new features/function in Javascript?

For adding features in Javascript you have to makeV8can compile this new feature.

#What feature we will add?

I will add simple function which doesn't exist normally in javascript, and i will call this function with nameGetFooand this function return what is pass it e.g"Hello World From C++"

v8::Local<v8::Value> GetFoo(v8::Local<v8::Context> context,
                            v8::Local<v8::Object> obj) {
  v8::Isolate* isolate = context->GetIsolate();
  v8::EscapableHandleScope handle_scope(isolate);

  // The 'foo_string' handle cannot be returned from this function because
  // it is not “escaped” with `.Escape()`.
  v8::Local<v8::String> foo_string =
      v8::String::NewFromUtf8(isolate, "foo").ToLocalChecked();

  v8::Local<v8::Value> return_value;
  if (obj->Get(context, foo_string).ToLocal(&return_value)) {
    return handle_scope.Escape(return_value);
  } else {
    // There was a JS exception! Handle it somehow.
    return v8::Local<v8::Value>();
  }
}

Now we created function calledGetFoowhen will execute? whenV8see this code in javascriptkarim_get_foo().

v8::Local<v8::Context> CreateShellContext(v8::Isolate* isolate) {
  // Create a template for the global object.
  v8::Local<v8::ObjectTemplate> global = v8::ObjectTemplate::New(isolate);
  // Bind the global 'print' function to the C++ Print callback.
  global->Set(isolate, "karim_get_foo", v8::FunctionTemplate::New(isolate, GetFoo));

    // GetFoo -> Here we binded function which we created before.
    // karim_get_foo -> new script we added in javascript, and it will trigger C++ function `GetFoo`
}

Now, when we write this javascript code

console.log( karim_get_foo("Hello World From C++") );

will print inconsole

Hello World From C++

#How V8 generate Machine code for Javascript code? let's see...

var x = "x variable";

what is generated machine code for this line of code?

Code
source_position
kind = FUNCTION
compiler
full-codegen
Instructions (size 164)
= 0
000001854AA38100
;; debug: position 0
000001854AA38101
000001854AA38104
000001854AA38105
000001854AA38106
000001854AA3810A
000001854AA3810B
000001A9E1DC5819
0 55
4889e5
push rbp
REX.W movq rbp,rsp
push rsi
push rdi
push [r13-0x58]
push rsi
1
4 56
5 57
6 41ff75a8
10 56
11 49ba1958dce1a9010000 REX.W movq r10
;; object: 000001A9E1DC5819 <FixedArray

and this machine code depend on yourMachine ProcessorandOperating System.

#nodejs #c++ #part3.1