code: function findMinSlack() {
      var result,
          eSlack = Number.POSITIVE_INFINITY;
      minLen.forEach(function(mle /* minLen entry */) {
        if (remaining.has(mle.u) !== remaining.has(mle.v)) {
          var mleSlack = rankUtil.slack(g, mle.u, mle.v, mle.len);
          if (mleSlack < eSlack) {
            if (!remaining.has(mle.u)) {
              result = {
                treeNode: mle.u,
                graphNode: mle.v,
                len: mle.len,
                reversed: false,
                weight: mle.weight
              };
            } else {
              result = {
                treeNode: mle.v,
                graphNode: mle.u,
                len: -mle.len,
                reversed: true,
                weight: mle.weight
              };
            }
            eSlack = mleSlack;
          }
        }
      });
  
      return result;
    }
docs: Finds the next edge with the minimum slack.