Global Objects
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 main.js which has the following code:
// Let's try to print the value of __filename console.log( __filename );
Now run the main.js to see the result:
$ node main.js
Based on the location of your program, it will print main file name as follows:
/web/com/1427091028_21099/main.js
__dirname
The __dirname represents the name of the directory that the currently executing script resides in.
Example
Create a js file named main.js which has the following code:
// Let's try to print the value of __dirname console.log( __dirname );
Now run the main.js to see the result:
$ node main.js
Based on the location of your program, it will print current directory name as follows:
/web/com/1427091028_21099
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 main.js which has the following code:
function printHello(){
console.log( "Hello, World!");
}
// Now call above function after 2 seconds
setTimeout(printHello, 2000);
Now run the main.js to see the result:
$ node main.js
Verify the output is printed after a little delay
Hello, World!
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 setTimeout() function.
Example
Create a js file named main.js which has the following code:
function printHello(){
console.log( "Hello, World!");
}
// Now call above function after 2 seconds
var t = setTimeout(printHello, 2000);
// Now clear the timer
clearTimeout(t);
Now run the main.js to see the result:
$ node main.js
Verify the output where you will not find anything printed.
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 main.js which has the following code:
function printHello(){
console.log( "Hello, World!");
}
// Now call above function after 2 seconds
setInterval(printHello, 2000);
Now run the main.js to see the result:
$ node main.js
Above program will execute function printHello() after every 2 second. Due to system limitation, this program can not be executed with Try it option so you can check it at your machine locally.
Global Objects
Following table gives a detail of few another objects which we use frequently in our applications. For a further detail you can refer to the official documentation.
| S.N. | 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. |