index.js

function(a,b,c){for(b=[1e3,60,60,24],a=new Date-a,c=0;a>2*b[c];a/=b[c++]);return~~a+" "+"m0second0minute0hour0day".split(0)[c]+"s ago"}

package.json

{
  "name": "timeAgo",
  "keywords": ["time", "chronological", "ago"]
}

timeAgo

function(
  a, // a Date object
  b, // placeholder
  c  // placeholder
){
  for (    // whittle the date down to biggest unit
    b = [  // an array containing the
      1e3, // ms in a second,
      60,  // seconds in a minute,
      60,  // minutes in an hour, and
      24   // hours in a day.
    ],
    a = new Date - a, // get ms since date passed.
    c = 0;            // initialize the cursor.
    a > 2 * b[c];     // while the 2 x time left exceeds the current unit,
    a /= b[c++]       // divide the time by the unit and increment.
  );                  // (note: the 2* above ensures the units are plural!)

  return ~~a +                 // the rounded remaining unit +
    " " +                      // a space + the unit name, which we get by
    "m0second0minute0hour0day" // taking a 0-delimited string of names
     .split(0)                 // splitting it by 0, and
     [c] +                     // taking the final cursor, +
    "s ago"                    // the plural and "ago"
}