Synchronous and Asynchronous Function - Node.js

Question

Hi ,

In this article i will teach you what is synchronous and asynchronous function in the node.js

What is Synchronous Function?

When a synchronous function is called, it completes executing before returning control to the client application.

It means the synchronous function will execute step by step like one after the another.It wont give the executing control before current process got execute.

In Synchronous way It waits for each operation to complete, after that only it executes the next operation.

What is Asynchronous Function?

When an application calls an asynchronous method, it can simultaneously execute along with the execution of the asynchronous method that performs its task. An asynchronous method runs in a thread separate from the main application thread. The processing results are fetched through another call on another thread.

In Asynchronous way It never waits for each operation to complete, rather it executes all operations in the first GO only.

Now we will see how synchronous and asynchronous function in node.js.

First take one scenario for reading file operation in using Synchronous and Asynchronous Function.

In the last article i used some example for synchronous and asynchronous.So,we take the example and see how these functions will executing.

Now our aim is to create a node for reading file in both synchronous and asynchronous way

First create one text file with contain some datas insode. File Name - > sample.txt- Inside Content -> This is the text file

Then Create a javascript file for accessing the read operation.

So i will create the file name as read.js

Synchronous Function In Node.js

var fs = require("fs");
console.log("start");
var content = fs.readFileSync("sample.txt","utf8");
console.log(content);
console.log("stoped"); 

Above code is written by using synchronous way.I already told synchronous function is a normal flow of execution.It will one by one.It wont give the control to another process before it completes.

So let see how it is working.

Step 1 : Include the fs library for using File IO Operation
Step 2: we printed the Start message (So it will print start message)
Step 3 :Then using synchronous file operation(readFileSync) we read a file as synchronously and store result in a content variable.
Step 4: Then we will print the content variable and get the result.
Step 5: Finally we will print the Stopped message.

So in this function is step by step process.It make us to wait until the current process got completed.

Output for synchronous function:

start
This is the text file
stoped 

Asynchronous Function in node.js

var fs = require("fs");
console.log("Start Reading");
fs.readFile("sample.txt","utf8",function(error,data){
 console.log(data);
});
console.log("stoped"); 

Node.js is mainly for non-blocking.It means it will not wait for any thing.So in this asynchronous function will use to write a non blocking function.

Let see the above code how it is working in asynchronous way.

Step 1 : Include the fs library for using File IO Operation
Step 2: we printed the Start message (So it will print start message)
Step 3 :Then using asynchronous file operation(readFile) we read a file as asynchronously and write a callback function will show the data and as well show the error message if any error comes.
Step 4: Finally we will print the Stopped message.

So how it works It will not work like synchronous function

See first it will print the Start message
Next we reading a file.So,in asychronous funtion will not wait until the file read operation completes.It will Start executing the next level.
It means next it will print the Stop message.
Finally when the file reading work is done then it will print the file datas.

Output for the Asynchronous Function

start
stoped
This is the text file

Also see the Below video for more understating about synchronous Function and Asynchronous function