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Relative time extension

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  1. /**
  2.  * Returns a description of this past date in relative terms.
  3.  * Takes an optional parameter (default: 0) setting the threshold in ms which
  4.  * is considered "Just now".
  5.  *
  6.  * Examples, where new Date().toString() == "Mon Nov 23 2009 17:36:51 GMT-0500 (EST)":
  7.  *
  8.  * new Date().toRelativeTime()
  9.  * --> 'Just now'
  10.  *
  11.  * new Date("Nov 21, 2009").toRelativeTime()
  12.  * --> '2 days ago'
  13.  *
  14.  * // One second ago
  15.  * new Date("Nov 23 2009 17:36:50 GMT-0500 (EST)").toRelativeTime()
  16.  * --> '1 second ago'
  17.  *
  18.  * // One second ago, now setting a now_threshold to 5 seconds
  19.  * new Date("Nov 23 2009 17:36:50 GMT-0500 (EST)").toRelativeTime(5000)
  20.  * --> 'Just now'
  21.  *
  22.  */
  23. Date.prototype.toRelativeTime = function(now_threshold) {
  24.   var delta = new Date() - this;
  25.  
  26.   now_threshold = parseInt(now_threshold, 10);
  27.  
  28.   if (isNaN(now_threshold)) {
  29.     now_threshold = 0;
  30.   }
  31.  
  32.   if (delta <= now_threshold) {
  33.     return 'Just now';
  34.   }
  35.  
  36.   var units = null;
  37.   var conversions = {
  38.     millisecond: 1, // ms    -> ms
  39.     second: 1000,   // ms    -> sec
  40.     minute: 60,     // sec   -> min
  41.     hour:   60,     // min   -> hour
  42.     day:    24,     // hour  -> day
  43.     month:  30,     // day   -> month (roughly)
  44.     year:   12      // month -> year
  45.   };
  46.  
  47.   for (var key in conversions) {
  48.     if (delta < conversions[key]) {
  49.       break;
  50.     } else {
  51.       units = key; // keeps track of the selected key over the iteration
  52.       delta = delta / conversions[key];
  53.     }
  54.   }
  55.  
  56.   // pluralize a unit when the difference is greater than 1.
  57.   delta = Math.floor(delta);
  58.   if (delta !== 1) { units += "s"; }
  59.   return [delta, units, "ago"].join(" ");
  60. };
  61.  
  62. /*
  63.  * Wraps up a common pattern used with this plugin whereby you take a String
  64.  * representation of a Date, and want back a date object.
  65.  */
  66. Date.fromString = function(str) {
  67.   return new Date(Date.parse(str));
  68. };

URL: http://github.com/jherdman/javascript-relative-time-helpers/blob/master/date.extensions.js

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