Concept of Buffer in Node.js

Net Javascript is Unicode encoded conveniently but not really good with binary data. When working with TCP streams or file systems, it is necessary to handle octal data streams. Node.js provides Buffer classes that allow raw data to be stored as an array of integers corresponding to external raw memory allocation V8 heap.

Buffer classes in Node.js are global classes and can be accessed in the application without declaring Buffer Modules by the require () method like other Modules.

Create buffers in Node.js

Buffers in Node.js can be built in many different ways.

Way 1

Syntax for creating a Buffer of size 10:

 var buf = new Buffer ( 10 ); 

Method 2

Syntax to create a Buffer from a given array:

 var buf = new Buffer ([ 10 , 20 , 30 , 40 , 50 ]); 

Method 3

The syntax for creating a Buffer from a given string and with arbitrary encoding:

 var buf = new Buffer ( "Hoc Nodejs tai QTM" , "utf-8" ); 

Although "utf8" is the default encoding, you can use other encodings such as "ascii", "utf8", "base64", .

Write data to Buffer in Node.js

Syntax

The syntax for writing a Buffer in Node.js is:

 buf . write ( string [, offset ][, length ][, encoding ]) 

Details about parameters

string - This is a string data written to the buffer.

offset - This is the index for the buffer to start recording there. The default value is 0.

length - The number of bytes recorded. The default is buffer.length.

encoding - Encoding is used. "utf8" is the default encoding.

Return value

The method will return the number of bytes written. If the memory in the buffer is not enough to satisfy the entire string, it will record part of the string.

The example illustrates how to write data to Buffer in Node.js

In this example, I use write () method to receive the parameter as string data to write that data to Buffer.

 buf = new Buffer ( 256 ); wool = buf . write ( "Hoc Nodejs at QTM" ); console . log ( "Tong so bytes of leather write:" + wool ); 

When the above program is executed will result:

 Tong so byte da ghi : 22 

Read data from Buffer in Node.js

Syntax

The syntax for reading data from Buffer in Node.js is as follows:

 buf . toString ([ encoding ][, start ][, end ]) 

Details about parameters

encoding - Is the encoding to use. Default encoding is 'utf8'.

start - Index to start reading operation, default value is 0.

end - Index to end the read operation, the default value is the length of the Buffer.

Return value

This method decodes and returns a string from the data encoded in the Buffer using a specific encoder.

The example illustrates how to read data from Buffer in Node.js

 buf = new Buffer ( 26 ); for ( var i = 0 ; i < 26 ; i ++) { buf [ i ] = i + 97 ; } console . log ( buf . toString ( 'ascii' )); // Ket via: abcdefghijklmnopqrstuvwxyz console . log ( buf . toString ( 'ascii' , 0 , 5 )); // Ket via: abcde console . log ( buf . toString ( 'utf8' , 0 , 5 )); // Ket via: abcde console . log ( buf . toString ( undefined , 0 , 5 )); // Su dung ma 'utf8', Ket via la: abcde 

When the above program is executed will result:

 abcdefghijklmnopqrstuvwxyz abcde abcde abcde 

Convert Buffer to JSON in Node.js

Syntax

To convert a Buffer in Node.js into a JSON object, you use the toJSON () method with the following syntax:

 buf . toJSON () 

Return value

This method returns a JSON representation for the given Buffer object.

The example illustrates how to convert Buffer to JSON

 var buf = new Buffer ( 'Simply Easy Learning' ); var json = buf . toJSON ( buf ); console . log ( json ); 

When the above program is executed will result:

 [ 83 , 105 , 109 , 112 , 108 , 121 , 32 , 69 , 97 , 115 , 121 , 32 , 76 , 101 , 97 , 114 , 110 , 105 , 110 , 103 ] 

Pair Buffers in Node.js

Syntax

To concatenate two or more Buffers into a Buffer in Node.js, you use concat () method as follows:

 Buffer . concat ( list [, totalLength ]) 

Details about parameters

list - Defines an array of Buffers used to pair into a Buffer.

totalLength - The total length of the buffers after being paired.

Return value

This method returns a new Buffer.

The example illustrates how to connect Buffers

 var buffer1 = new Buffer ( 'The software provides a new version of the database ' ); var buffer2 = new Buffer ( 'for people' ); var buffer3 = Buffer . concat ([ buffer1 , buffer2 ]); console . log ( "The content of buffer3 is:" + buffer3 . toString ()); 

When the above program is executed will result:

 Noi dung cua buffer3 la : QTM cung cap loat bai huong dan mien phi cho tat ca moi nguoi 

Compare Buffers in Node.js

Syntax

To compare two Buffers in Node.js, you use the compare () method as follows:

 buf . compare ( otherBuffer ); 

Details about parameters

otherBuffer - Another Buffer to be compared to a Buffer named buf.

Return value

Returns a numerical value that represents this Buffer to stand before, after, or the same order as the other Buffer.

The example illustrates how to compare two Buffers in Node.js

 var buffer1 = new Buffer ( 'ABC' ); var buffer2 = new Buffer ( 'ABCD' ); var result = buffer1 . compare ( buffer2 ); if ( result < 0 ) { console . log ( buffer1 + "capacitance" + buffer2 ); } else if ( result == 0 ) { console . log ( buffer1 + "supply and retrieve the elephant" + buffer2 ); } else { console . log ( buffer1 + "use later" + buffer2 ); } 

When the above program is executed will result:

 ABC dung truoc ABCD 

Copy the Buffer in Node.js

Syntax

To copy the Buffer in Node.js, you use the copy () method as follows:

 buf . copy ( targetBuffer [, targetStart ][, sourceStart ][, sourceEnd ]) 

Details about parameters

targetBuffer - Buffer object, this is where the Buffer will be copied.

targetStart - Number format, default is 0.

sourceStart - Number format, the default is 0.

sourceEnd - Number format, the default is the length of the buffer.

Return value

This copy () method does not return any values.

The example illustrates how to copy Buffer

 var buffer1 = new Buffer ( 'ABC' ); // Why is the buffer buffer var buffer2 = new Buffer ( 3 ); buffer1 . copy ( buffer2 ); console . log ( "Content file buffer2 is:" + buffer2 . toString ()); 

When the above program is executed will result:

 Noi dung cua buffer2 la : ABC 

Split the Buffer in Node.js

Syntax

To create a child Buffer of a Buffer in Node.js, use the slice () method as follows:

 buf . slice ([ start ][, end ]) 

Details about parameters

start - Number format, the default value is 0.

end - Number format, the default value is buffer.length

Return value

Returns a new buffer that references the same memory area as the old Buffer.

For example

 var buffer1 = new Buffer ( 'VietNamVoDoi' ); // Divide the grapefruit buffer var buffer2 = buffer1 slice ( 0 , 7 ); console . log ( "Content file buffer2 is:" + buffer2 . toString ()); 

When the above program is executed will result:

 Noi dung cua buffer2 la : VietNam 

Length Buffer in Node.js

Syntax

To get the length (equal to the byte value) of a Buffer in Node.js, you use the following length attribute:

 buf . length ; 

Return value

Returns the length in bytes of a Buffer.

For example

 var buffer = new Buffer ( 'VietNamVoDoi' ); // Due to the persistent buffer console . log ( "Due to the buffer is:" + buffer . length ); 

When the above program is executed will result:

 Do dai cua buffer la : 12 

According to Tutorialspoint

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