Which is the global object of node?

The global object of node is "global". The most fundamental role of global is to serve as the host of global variables; and all global variables (except global itself) are attributes of the global object. Global properties can be accessed directly in Node.js without including it in the application.

The operating environment of this tutorial: Windows 7 system, nodejs version 16, DELL G3 computer.

There is a special object in JavaScript called the global object (Global Object). It and all its properties can be accessed anywhere in the program, that is, global variables.

In browser JavaScript, window is usually a global object, while the global object in Node.js is global. All global variables (except global itself) are properties of the global object. .

In Node.js we can directly access global properties without including it in the application.

Global objects and global variables

The most fundamental role of global is to serve as the host of global variables. According to the definition of ECMAScript, variables that meet the following conditions are global variables:

• Variables defined in the outermost layer;

• global Properties of objects;

• Implicitly defined variables (variables with direct assignment are not defined).

When you define a global variable, the variable also becomes a property of the global object, and vice versa. It should be noted that in Node.js you cannot define variables at the outermost level, because all user code belongs to the current module, and the module itself is not the outermost context.

Note: It is best not to use var to define variables to avoid introducing global variables, because global variables will pollute the namespace and increase the risk of code coupling.

1, __filename

Create new global.js with the following content:

console.log( __filename );

Run as follows:

node global.js __filename=/root/node_test/global.js

2 , __dirname

Create a new dirname.js with the following content:

console.log(__dirname);

Run as follows:

node  dirname.js /root/node_test

3. setTimeout(cb, ms)

setTimeout(cb, ms) The global function executes the specified function (cb) after the specified number of milliseconds (ms). :setTimeout() only executes the specified function once.

Returns a handle value representing the timer.

4. clearTimeout(t)

clearTimeout(t) global function is used to stop a timer previously created through setTimeout(). The parameter t is the timer created through the setTimeout() function.

5. setInterval(cb, ms)

setInterval(cb, ms) The global function executes the specified function (cb) after the specified number of milliseconds (ms).

Returns a handle value representing the timer. The timer can be cleared using the clearInterval(t) function.

The setInterval() method will continue to call the function until clearInterval() is called or the window is closed.

6. console

The methods of the console object are the same as the traditional js printing methods in the browser, which are omitted.

7. process

It is an object used to describe the current Node.js process status and provides a simple interface with the operating system. Usually when you write a local command line program, you have to deal with it.

• exit
  Triggered when the process is ready to exit.

• beforeExit
  This event is triggered when node clears the event loop and there are no other arrangements. Normally node exits when no processes are scheduled, but the 'beforeExit' listener can be called asynchronously so that node continues execution.

• uncaughtException
  This event is triggered when an exception bubbles back to the event loop. If a monitor is added to the exception, the default action (print the stack trace and exit) will not occur.

• Signal event
  Triggered when the process receives a signal. For the signal list, see the standard POSIX signal names, such as SIGINT, SIGUSR1, etc.

For more node-related knowledge, please visit: nodejs tutorial!

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