Abbreviates full IPv6 addresses by removing the leading "0" and collapsing longest consecutive run of 16-bit zeros down to "::".

abbreviate_ipv6.js

/* Abbreviate full ipv6 address
 * By Brent Stees (http://facebook.com/brent.stees), 2014
 * MIT Licenced, see http://www.opensource.org/licenses/mit-license.php */

function abbreviate_ipv6(ip){
  if(ip.indexOf("::") == -1) {

    // needs to be abbreviated

    // remove leading zeros
    ip = ip.replace(/^0+/,'').replace(/\:0/g,':');

    // find longest run of consecutive zeros

    var sixteens = ip.split(':'),
          max = 0,
          current = 0,
          replace = "";

    for(i=0; i<sixteens.length; i++) {
      // test for non-numbers, this is so we can do an exact match later
      if (!/\D/.test(sixteens[i])) {
        sixteens[i] = parseInt(sixteens[i],10);
      } else {
        // do nothing        
      }

      // check for "0" and increment
      if (sixteens[i] === 0){
        current++;
      } else {
        max = Math.max(current,max);
        current = 0;
      }
    }

    // build replace string
    for (i=0; i<max; i++){
      replace += ":0";
    }

    // replace
    return sixteens.join(':').replace(replace,":");
    
  } else {

    // do nothing and return original value of ip
    return ip;

  }
}

// abbreviate_ipv6("FE02:0000:0000:0050:0000:0000:0000:0101");