Blocking and Non-Blocking I/O

blocking.js

//BLOCKING
var post = db.query('SELECT * FROM posts where id = 1');
// processing from this line onward cannot execute
// until the line above completes
doSomethingWithPost(post);
doSomethingElse();

//NON-BLOCKING
callback = function(post) {
// this will only execute when the db.query function returns.
doSomethingWithPost(post);
};
db.query('SELECT * FROM posts where id = 1', callback);
// this will execute independent of the returned status
// of the db.query call.
doSomethingElse();