Node.js – Global Objects

Node.js – Global Objects

Node.js global objects are global in nature and they are available in all modules. We do not need to include these objects in our application, rather we can use them directly. These objects are modules, functions, strings and object itself as explained below.

__filename

The __filename represents the filename of the code being executed. This is the resolved absolute path of this code file. For a main program, this is not necessarily the same filename used in the command line. The value inside a module is the path to that module file.

Example

Create a js file named app.js with the following code −

// Let's try to print the value of __filename
console.log( __filename );

Now run the app.js to see the result −

$ node app.js

Based on the location of your program, it will print the main file name as follows −

/web/com/1427091028_21099/app.js

__dirname

The __dirname represents the name of the directory that the currently executing script resides in.

Example

Create a js file named app.js with the following code −

// Let's try to print the value of __dirname
console.log("your current directory name is :" + __dirname);

Now run the app.js to see the result −

$ node app.js

Based on the location of your program, it will print current directory name as follows −

your current directory name is :D:Node.jsnode-programs

setTimeout(cb, ms)

The setTimeout(cb, ms) global function is used to run callback cb after at least ms milliseconds. The actual delay depends on external factors like OS timer granularity and system load. A timer cannot span more than 24.8 days.
This function returns an opaque value that represents the timer which can be used to clear the timer.

Example

Create a js file named app.js with the following code −

function printHello() {
console.log( "two seconds over");
}
// Now call above function after 2 seconds
setTimeout(printHello, 2000);

Now run the app.js to see the result −

$ node app.js

Verify the output is printed after a little delay.

two seconds over

clearTimeout(t)

The clearTimeout(t) global function is used to stop a timer that was previously created with setTimeout(). Here t is the timer returned by the setTimeout() function.

Example

Create a js file named app.js with the following code −

function printHello() {
console.log( "Two Seconds Over");
}
// Now call above function after 2 seconds
var timer = setTimeout(printHello, 2000);
// Now clear the timer
setTimeout(function(){
console.log("timer stopped before two seconds!");
clearTimeout(timer);
},1000)

Now run the app.js to see the result −

$ node app.js

Verify the output where you will not find anything printed.

timer stopped before two seconds!

setInterval(cb, ms)

The setInterval(cb, ms) global function is used to run callback cb repeatedly after at least ms milliseconds. The actual delay depends on external factors like OS timer granularity and system load. A timer cannot span more than 24.8 days.
This function returns an opaque value that represents the timer which can be used to clear the timer using the function clearInterval(t).

Example

Create a js file named app.js with the following code −

var x=0;
function counter() {
x++;
console.log(x);
}
// Now call above function after 1 seconds
var countdown = setInterval(counter, 1000);
setTimeout(function(){
clearInterval(countdown);
},11000)

Now run the app.js to see the result −

$ node app.js

The above program will execute counter of 1 to 10

1
2
3
4
5
6
7
8
9
10

Global Objects

The following table provides a list of other objects which we use frequently in our applications. For a more detail, you can refer to the official documentation.

Sr.No. Module Name & Description
1 Console

Used to print information on stdout and stderr.

2 Process

Used to get information on current process. Provides multiple events related to process activities.

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