Read Evaluate Print Line.
node js allows us to write code directly into an environment that executes it immediately and is
useful when you quickly try out things. The Javascript Console inside chrome developer tool is also a REPL.
Open up the terminal
node
and tap enter.
10+10; //in terminal - REPL
new Date();
//Shift + enter to write same block of code in new line.
function a(){
return 'test';
}
Everything that you type in the REPL will be saved in the session. To save this session into a file
you will have to write .save fileName.js all the REPL code will be imported as fileName.js
fs.read('storyBook.txt','utf8',function(err,content){console.log(content);})
Same as saving a session we can load a javascript file too.
.load jsFile.js
//now the function and code that are in the jsFile.js will be available in the REPL
A software that serves to files and data. apache,nginx serves files and data and run various server executable code.
In Nodejs you will have to build your server.
var http = require('http');//http module contains all the available methods used to create server.
var host = '127.0.0.1';
var port = '9000';
var server = http.createServer(function (req, res) {
res.writeHead(200, {
'Content-Type': 'text/html'
});//sets the header and status code of the content we are about to serve.
res.end('<h1>Hello world</h1>');
}).listen(port, host, function () {
console.log('Dev server started on http://' + host + ':' + port);
});
Run you server by
node build-server.js
In node js you will have to build you own server to parse you html,image etc file to the browser
Here's a sample code
var http = require('http'),
fs = require('fs'),//fs or a filesystem module allows us to read write and play with the file
path = require('path'),//path module help us to construct the path module.
host = '127.0.0.1',
port = '9000';
var commonMimes = {
".htm": "text/html",
".css": "text/css",
".js": "text/javascript",
".jpeg": "image/jpeg",
".jpg": "image/jpeg",
".png": "image/png",
".gif": "image/gif",
".html": "text/html"
};
var server = http.createServer(function (req, res) {
var filePath = req.url === '/' ? './index.html' : '.' + req.url; // if the uri is empty open index.html or request the requested file
//check if the file exists or not
fs.exists(filePath, function (fileExists) {
if (fileExists) {
//fetch the extension name of a file using the path module and parsing it's mime type by our jsonObject.
var contentType = commonMimes[path.extname(filePath)];
fs.readFile(filePath, function (error, content) {
if (error) {
res.writeHead(500);
res.end();
} else {
res.writeHead(200, {'Content-Type': contentType});
res.end(content, 'utf-8');
}
});
} else {
res.writeHead(404);
res.end("Sorry we count not find the file you requested");
}
})
}).listen(port, host, function () {
console.log('Dev server started on http://' + host + ':' + port);
});
this function buffers up every file to the memory before serving them out. The files are read into the buffer and only when the file is read completely it is flushed out to the response object. This slow down things and consumes the server resources badly
These are like pipelines to your app which can control and allow data to flow through your app whithout holding it in buffer. So Instead of waiting for files to buffer files are streamed out to the user as it is being read. This cut's down the server and makes the serving very very efficiency.
We will modify the file serving code above and make it able to stream.
var http = require('http'),
fs = require('fs'),//fs or a filesystem module allows us to read write and play with the file
path = require('path'),//path module help us to construct the path module.
host = '127.0.0.1',
port = '9000';
var commonMimes = {
".htm": "text/html",
".css": "text/css",
".js": "text/javascript",
".jpeg": "image/jpeg",
".jpg": "image/jpeg",
".png": "image/png",
".gif": "image/gif",
".html": "text/html"
};
var server = http.createServer(function (req, res) {
var filePath = req.url === '/' ? './index.html' : '.' + req.url; // if the uri is empty open index.html or request the requested file
//check if the file exists or not
fs.exists(filePath, function (fileExists) {
if (fileExists) {
//fetch the extension name of a file using the path module and parsing it's mime type by our jsonObject.
var contentType = commonMimes[path.extname(filePath)];
res.writeHead(200, {
'Content-Type': contentType
});
var streamFile = fs.createReadStream(filePath).pipe(res);//the create read Stream function reads the file in a streaming mode.
//Handling any possible errors that might be possible during streaming a file.
streamFile.on('error', function () {
res.writeHead(500);
res.end();
})
} else {
res.writeHead(404);
res.end("Sorry we count not find the file you requested");
}
})
}).listen(port, host, function () {
console.log('Dev server started on http://' + host + ':' + port);
});
(mysql,microsoft sql server) etc are relation database management system have been for around 20 years.
Over the past few years the storage and consumption of data has sky rocketed beyond our imagination.
All of this has given rise to a term big data which refers to the storage and processing of stream amount of data.
The relational db like mysql is not suitable for handling extreme amount of data.
Additionally the data these days does not confirm into being in a decided schema and since RDBMS requires you to have a fixed schema it does not fit well into a flexible development environment.
So one of the best solution out there is a breed of nosql database mongodb.
mongo derived from the word humongo (allows you to deal with humongous amount of data) in simple way.
Instead of row and columns mongodb stores data in documents using key value pair.
{
"name":"selvesan",
"email":"[email protected]"
}
This is known as Bson which is based like json and used like json
{
"name":['ram','shyam'],
"address":{...},{...} // one to many relationships.
}
{
_id:ObjectId('....')
}
table > collection row > Document column > Fileds
select * from table where condition
db.table.find({
email:'[email protected]'
})
- High performance reads and write.
- Very highly & Easily scalable.
- Document Database is schema less.
- Json style documents
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