1.
Prepared By:
Prof. Bareen Shaikh
Department of Computer
Science,
MIT ACSC,ALNDI(D), PUNE
NodeJs Modules

2.
Topics
 3.1 Functions
 3.2 Buffer
 3.3 Module and ModuleTypes
 3.4 Core Module, Local Module
 3.5 Directories as module
 3.5 Module. exports

3.
Functions
 Functions are first class citizens in Node's JavaScript, similar to
the browser's JavaScript.
 A function can have attributes and properties also.
 It can be treated like a class in JavaScript.
Example:
function Sum(x,y) {
console.log(x+y);
}
Sum(505,606);

4.
Buffers
 Definition: Buffer is an object property on Node’s global object, which is heavily
used in Node to deal with streams of binary data. It is globally available.
 JavaScript is Unicode friendly.
 But not dealing with binary data.
 Binary data is needed while handling withTCP or file system.
 For this NODEJS provide Buffer class.
 Buffer class store raw data similar as storing integer in array.
 But it will be stored at raw memory allocation outside of V8 heap.
 V8 is the default JavaScript engine which powers Node and Google Chrome

5.
Creating Buffer
Following are the ways to create buffers:
 Buffer.from()
 Using constructor
 Buffer.alloc()
 Buffer.allocUnsafe()
Buffer.from()
 Buffer.from is used to create a buffer from either an array, a string, or
from a buffer itself.
 Buffer.from(‘Node.js’)
outputs <Buffer 4e 6f 64 65 2e 6a 73>
 Using Constructor
var buff=new Buffer(15);
var buff=new Buffer(“hello”);

6.
Creating Buffer
 Buffer.alloc()
 Buffer.alloc takes a size (integer) as an argument and returns a new
initialized buffer of the specified size (i.e., it creates a filled buffer
of a certain size).
 >Buffer.alloc(8)
outputs <Buffer 00 00 00 00 00 00 00 00> //Here we have an 8-
byte buffer, and every bit is prefilled
with 0.

7.
Creating Buffer
 Buffer.allocUnsafe()
 It takes in size as an argument and returns a new buffer that is non
initialized.
 It can contain some old or sensitive data out of your memory.
 This method is faster than the Buffer.alloc(), but use it carefully.
 >Buffer.allocUnsafe(8)
output <Buffer 18 cd 7e 02 00 00 00 00>
 We can see that there is some information left in our buffer
 In order to protect our sensitive information we need to prefill buffer
 Do that by using the fill() method.
 >Buffer.allocUnsafe(8).fill()
outputs <Buffer 00 00 00 00 00 00 00 00>

8.
Reading from Buffer
 Syntax
buf.toString([encoding][, start][, end]) Parameters
 encoding − Encoding to use. 'utf8' is the default encoding.
 start − Beginning index to start reading, defaults to 0.
 end − End index to end reading, defaults is complete buffer.
 ReturnValue
This method decodes and returns a string from buffer data encoded
using the specified character set encoding.

9.
Reading from Buffer Example
 > Buffer.from('Node.js')
<Buffer 4e 6f 64 65 2e 6a 73>
 > Buffer.from('Node.js').toString()
'Node.js'
 > Buffer.from('Node.js').toString('ascii')
'Node.js‘ //for 7-bitASCII data only
 > Buffer.from('Node.js').toString('utf8')
'Node.js‘ //multibyte encoded Unicode characters
 > Buffer.from('Node.js').toString('base64')
'Tm9kZS5qcw==‘ //Base64 encoding
 > Buffer.from('Node.js').toString('hex')
'4e6f64652e6a73‘ // encode each byte as two hexadecimal characters

10.
Writing to a Buffer
 Syntax
buf.write(string[, offset][, length][, encoding]) Parameters
 string −This is the string data to be written to buffer.
 offset −This is the index of the buffer to start writing at. Default value
is 0.
 length −This is the number of bytes to write. Defaults to buffer.length.
 encoding − Encoding to use. 'utf8' is the default encoding.
 ReturnValue
This method returns the number of octets written. If there is not enough
space in the buffer to fit the entire string, it will write a part of the string.
 Example
buf = new Buffer(25);
len = buf.write(“HelloWorld“,”utf-8”);
console.log(“ written : "+ len);

11.
Buffer example
 const str="bareen";
 > const buf=Buffer.from(str);
 > console.log('String Data',str)
OUTPUT : String Data bareen
 > console.log('String Data',str.length)
OUTPUT : String Data 6
 > console.log('String Data',buf)
OUTPUT : String Data <Buffer 62 61 72 65 65 6e>
 > console.log('String Data',buf.length)
OUTPUT : String Data 6

12.
Buffer Functions
 Compare Buffers
buf.compare(otherBuffer);
 otherBuffer −This is the other buffer which will be compared
with buf
 ReturnValue
Returns a number indicating whether it comes before or after or is
the same as the otherBuffer in sort order.
 Example

13.
Buffer Functions
 Compare Buffers Example
var buffer1 = new Buffer('ABC');
var buffer2 = new Buffer('ABCD');
var result = buffer1.compare(buffer2);
if(result < 0) {
console.log(buffer1 +" comes before " + buffer2);
}
else if(result === 0) {
console.log(buffer1 +" is same as " + buffer2);
}
else {
console.log(buffer1 +" comes after " + buffer2);
}

14.
Buffer Function
 Copying a Buffer
buf.copy(target[,target start[,sourcestart[,sourceend]]]);
 target −This is the target buffer in which to copy.
 target start- it is integer from where to start writing in buffer
 Source start-it is integer from which to begin copy in buffer
 Source end-it is integer where to stop copying in buffer
 ReturnValue
Returns a number indicating number bytes copied.

15.
Buffer Functions
 Copying Buffers Example
var buffer1 = Buffer.allocUnsafe(26);
var buffer2 = Buffer. allocUnsafe(26).fill(‘!’);
console.log(buffer1.toString());
console.log(buffer1.toString());
for(let i=0;i<26;i++){
buffer1[i]=i+97;
}
buffer1.copy(buffer2,8,16,20);
console.log(buffer2.toString());
}

16.
When to use Buffer
 Buffers are very useful when we need to read things like an image
from aTCP stream, a compressed file, or any other form of binary
data.
 Buffers are heavily used in streams in Node.
 Note:Just like arrays and strings, for buffer, we can use operations
like slice, indexOf, and many others.With some difference they are
to be used.

17.
Thank You