gistfile1.js

var fs = require('fs');

// read a file
function read_the_file(filename, callback) {

    // begin by reading a file
    fs.readFile(filename, function (err, contents) {

        // an error occurred, i.e. the file was not found.
        // instead of throwing an error, skip the other 
        // functions and directly invoke the callback
        // function and provide the error object
        if (err) return callback(err);

        // continue
        read_data_from_db(null, contents, callback);
    });

} // read_the_file()

// this function would hold the next step
function read_data_from_db(err, contents, callback) {
    /* logic here */
} // read_data_from_db()


// this function call could originate from somewhere else
// in your code.
read_the_file('/some/file', function (err, result) {
    
    // don't throw the error, just log it (just because)
    if (err) {
        console.log(err);
        return;
    }

    // do something with the result
});