ago(date) function to return a brief "ago" string.

ago.js

var second = 1e3;
var minute = 6e4;
var hour = 36e5;
var day = 864e5;
var week = 6048e5;

function ago(diff) {
    var unit, num;
    if (diff <= second) {
    	unit = 's';
    	num = 1;
    } else if (diff < minute) {
    	unit = 's';
    	num = diff / second;
    } else if (diff < hour) {
    	unit = 'm';
    	num = diff / minute;
    } else if (diff < day) {
    	unit = 'h';
    	num = diff / hour;
    } else if (diff < week) {
    	unit = 'd';
    	num = diff / day;
    } else {
    	unit = 'w';
    	num = diff / week;
    }
    return num + unit;
}