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NodeJs Modules.pdf

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NodeJs Modules.pdf

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

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