How to use the vega-dataflow.tupleid function in vega-dataflow

function update(t) {
    var p, idx;

    if (res.length < num) {
      res.push(t);
    } else {
      idx = ~~((cnt + 1) * random());
      if (idx < res.length && idx >= cap) {
        p = res[idx];
        if (map[tupleid(p)]) out.rem.push(p); // eviction
        res[idx] = t;
      }
    }
    ++cnt;
  }

pulse.visit(pulse.MOD, function(t) {
      var id = tupleid(t),
          k0 = cache.get(id),
          k1 = key(t);
      if (k0 === k1) {
        subflow(k1).mod(t);
      } else {
        cache.set(id, k1);
        subflow(k0).rem(t);
        subflow(k1).add(t);
      }
    });
  } else if (pulse.changed(pulse.MOD)) {

pulse.visit(pulse.REM, function(t) {
    var id = tupleid(t);
    out.rem.push(lut[id]);
    lut[id] = null;
  });

pulse.visit(pulse.REM, function(t) {
      var id = tupleid(t);
      if (map[id]) {
        map[id] = -1;
        out.rem.push(t);
      }
      --cnt;
    });

pulse.visit(pulse.MOD, function(t) {
      subflow(cache.get(tupleid(t))).mod(t);
    });
  }

    pulse.visit(pulse.SOURCE, function(t) { lut[tupleid(t)] = 1; });

pulse.visit(pulse.REM, function(t) {
      var id = tupleid(t);
      out.rem.push(lut[id]);
      lut[id] = null;
    });

pulse.visit(pulse.REM, function(t) {
    var id = tupleid(t),
        k = cache.get(id);
    if (k !== undefined) {
      cache.delete(id);
      subflow(k).rem(t);
    }
  });

tree.each(function(node) {
      var t = node.data,
          p = node.parent && node.parent.data;
      if (p && lut[tupleid(t)] && lut[tupleid(p)]) {
        out.add.push(ingest({source: p, target: t}));
      }
    });
    this.value = out.add;

links.forEach(function(link) {
      if (lut[tupleid(link.source)] || lut[tupleid(link.target)]) {
        out.mod.push(link);
      }
    });
  }