A JavaScript engine

$ node
> console.log( "Hello, world" );
Hello, world
> 2+3
5
> 0 == ""
true

A JavaScript engine

• Built on V8
• which is Chrome's engine
• so it's reasonably fast

A JavaScript engine

• With a module system

# namethatday.js

var weekday = require( "weekday" );

var day = weekday( process.argv[2] );

console.log( day.name );

A JavaScript engine

• With a module system

$ node namethatday.js 5
Friday

A set of libraries

A set of libraries

• Lots of them
• Most are very small
• Often a single function

A set of libraries

• For example:

concat-array

Takes a string and an array of strings and concatenates the first string to each string in the array.

A set of libraries

var ca = require('concat-array');

var arr = ['shrimp', 'tron'];
console.log(ca.concatArray('jumbo', arr));

# prints [ 'jumbo shrimp', 'jumbo tron' ]

A set of libraries

• For web sites, there is express:

var express = require('express');
var app = express();

app.get('/', function(req, res){
  res.send('Hello World');
});

app.listen(3000);

A set of libraries

• Express (and Connect) support "middleware"
• Little snippets of code that modify or handle requests

A set of libraries

var express = require('express');
var app = express();

app.use(express.basicAuth("testUser", "testPass"));

app.get('/', function(req, res) {
  res.send('Hello World');
});

app.listen(3000);

Going to blow your mind

"Everything runs in parallel, except your code"

Going to blow your mind

"Everything runs in parallel, except your code"

• Callbacks instead of threads
• "Async" programming

Going to blow your mind

"Everything runs in parallel, except your code"

Pros:

• Highly scalable, yet...
• ...single-threaded

Going to blow your mind

"Everything runs in parallel, except your code"

Cons:

Going to blow your mind

• All IO is async, via callbacks

var fs = require('fs');

function doSomething(err, contents) {
    if (err) throw err;
    console.log(contents);
}

fs.readFile('myfile.txt', 'utf8', doSomething);

Going to blow your mind

• Often callbacks are inline

var fs = require('fs');

fs.readFile('myfile.txt', 'utf8', function(err, data) {
    if (err) throw err;
    console.log(data);
});

Going to blow your mind

• Don't throw or return - instead call callbacks

$ node cp.js myfile.txt myfile2.txt
Copied 4 bytes.

Going to blow your mind

• Don't throw or return - instead call callbacks

copyFile( process.argv[2], process.argv[3],
    function(err, length) {
        if (err) console.log(err);
        else console.log( "Copied " + length + " bytes." );
    }
);

Going to blow your mind

• Don't throw or return - instead call callbacks

function copyFile(infn, outfn, callback) {
    fs.readFile( infn, function(err, data) {
        if (err) callback(err);
        else fs.writeFile( outfn, data, function(err) {
              if (err) callback(err);
              else callback(null, data.length);
}); }); }

Going to blow your mind

• Welcome to Callback Hell

                                                            });
                                                        });
                                                    });
                                                });
                                            });
                                        });
                                    });
                                });
                            });
                        });
                    });
                });
            });
        });
    });
});

Tips for writing node code

1. Don't forget you are writing code

Tips for writing node code

1. Don't forget you are writing code
• Write short functions
• Write tests
• Give things names
2. There is no 2

More info

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Blog	artificialworlds.net/blog
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