JavaScript to Output Text Based on User's Current Time

Try following piece of Javascript code:

var today = new Date()
var curHr = today.getHours()

if (curHr < 12) {
  console.log('good morning')
} else if (curHr < 18) {
  console.log('good afternoon')
} else {
  console.log('good evening')
}

var data = [
    [0, 4, "Good night"], 
    [5, 11, "Good morning"],          //Store messages in an array
    [12, 17, "Good afternoon"],
    [18, 24, "Good night"]
],
    hr = new Date().getHours();

for(var i = 0; i < data.length; i++){
    if(hr >= data[i][0] && hr <= data[i][1]){
        console.log(data[i][2]);
    }
}

Demo: http://jsfiddle.net/DerekL/we8Ty/

This is just a small variation of the solution from Derek 朕會功夫 above.
I felt the array is cleaner than a bunch of if statements.
If you work the hours backwards, you don't need a start AND end hour.
Also, once you make a match, I added a break; to kick out early.

var data = [
    [22, 'Working late'],
    [18, 'Good evening'],
    [12, 'Good afternoon'],
    [5,  'Good morning'],
    [0,  'Whoa, early bird']
],
hr = new Date().getHours();
for (var i = 0; i < data.length; i++) {
    if (hr >= data[i][0]) {
        console.log(data[i][1])
        break;
    }
}