Learn How to Work With Global Objects in NodeJS

In this article, we are going to discuss the global objects which are present in the various modules of node.js. The most interesting thing about global objects is that when we are using these objects in our application, then we need not to include these objects i.e. we can call or use these objects directly. Global objects could be the modules, functions, strings and an object itself. Let us understand about the types of the global objects with the following examples.

Global Strings

• __filename: – The __filename signifies the filename of the code which is under execution. It is nothing but the resolved absolute path of the code file. When working with a main program then it is not unavoidably the same filename which is used in the command line. The path to the module file is the value inside a module as shown below.

// Command to print the value of __filename on the console.

console.log( __filename );

When we execute the above code, then we will observe the absolute file path is printed on the console as shown below.

C:\odesk\Abhishek Thakur\NodeJS\GlobalObjects\hello-world-server.js

• __dirname: – The __dirname signifies the name of the directory that exists in the executing script. When we log the value of this global string, then it will print the absolute directory path where the script file exists on the machine drive as shown below.

//Command to print the value of __dirname on the console.

console.log( __dirname );

When we execute the above code, then we will observe the absolute file path at the directory level is printed on the console as shown below.

C:\odesk\Abhishek Thakur\NodeJS\GlobalObjects

Global Functions

• Function setTimeout (callback, milliseconds): – The ‘setTimeout (callback, milliseconds)’ is the global function which is used to run callback after waiting for the given time in the milliseconds. These are the two parameters which are passed to this function. The other factors on which the time delay depends are the OS timer granularity and the system load. The maximum time to which such a timer could span is 24.8 days. The following is an example of the timer function where it calls back a function and prints a string present inside that function after 3000 ms (i.e. 3 seconds).

function printHelloWorld(){
   console.log ("Hello, welcome to the World of global objects in Node.js!");
}
// Now call above function after 3 seconds
setTimeout(printHelloWorld, 3000);

When we execute the above code, then we will observe the string is printed on the console after 3 seconds delay as shown below.

Hello, welcome to the World of global objects in Node.js!

• Function clearTimeout (time): – The ‘clearTimeout (time)’ is a global function which is used to stop a timer which was previously created with the help of the ‘setTimeout ()’ function. Here. the parameter time is the timer which is returned by the ‘setTimeout ()’ function. The following is an example of the clearTimeout function which will clear the timer created by the setTimeout function.

function printHelloWorld(){
   console.log( "Hello, welcome to the World of global objects in Node.js!");
}
// Now call above function after 3 seconds
var time = setTimeout(printHelloWorld, 3000);

//To clear the timer
clearTimeout(time);

When we execute the above code, then we will observe that nothing is printed on the console even after 3 seconds delay as the timeout timer is cancelled by the clearTimeout function.

• Function setInterval (callback, milliseconds): – The ‘setInterval (callback, milliseconds)’ is the global function which is used to run the callback repetitively after the time interval given in the milliseconds. The other factors on which the time delay depends are the OS timer granularity and system load. The maximum time to which such a timer could span is 24.8 days. The following is an example of the setInterval function, where it calls back a function and prints a string present inside that function repetitively after every 3000 ms (i.e. 3 seconds). Also, it returns an opaque value that signifies the timer. This timer can be cleared by using the function ‘clearInterval (timer)’.

function printHelloWorld(){
   console.log( "Hello, welcome to the World of global objects in Node.js!");
}
//call the above function after 3 seconds repetitively 
setInterval(printHelloWorld, 3000);

When we execute the above code, then we will observe that the string is printed on the console after every 3 seconds on the console as shown below.

Hello, welcome to the World of global objects in Node.js!
Hello, welcome to the World of global objects in Node.js!
Hello, welcome to the World of global objects in Node.js!
Hello, welcome to the World of global objects in Node.js!

Global Objects
The following table shows a list of other objects which can be used very often in our applications.

1. Console Methods: –In Node.js, a console is a global object which can be used to print different levels of messages to stdout and stderr. The following are the various built-in methods which can be used for printing informational, warning, and error messages.

Example of console methods: –

console.log( __dirname );
console.info( __filename );

2. Process Methods: – The process object is used to get the information on current process. It provides multiple events and methods related to the process activities. Using these methods, we can get the better control over system interactions. The following are some of the Process methods which are frequently used in the application.

Source code for the various global objects in Nodejs
Conclusion: –
In this article, we discussed the various global objects in Node.js which can be referred to directly without importing modules in Node.js along with the supporting examples.