Function bindKey

external/.d3.js:1857–1899

(parent, group, enter, update, exit, data, key)

}

function bindKey(parent, group, enter, update, exit, data, key) {
  var i,
      node,
      nodeByKeyValue = new Map,
      groupLength = group.length,
      dataLength = data.length,
      keyValues = new Array(groupLength),
      keyValue;

  // Compute the key for each node.
  // If multiple nodes have the same key, the duplicates are added to exit.
  for (i = 0; i < groupLength; ++i) {
    if (node = group[i]) {
      keyValues[i] = keyValue = key.call(node, node.__data__, i, group) + "";
      if (nodeByKeyValue.has(keyValue)) {
        exit[i] = node;
      } else {
        nodeByKeyValue.set(keyValue, node);
      }
    }
  }

  // Compute the key for each datum.
  // If there a node associated with this key, join and add it to update.
  // If there is not (or the key is a duplicate), add it to enter.
  for (i = 0; i < dataLength; ++i) {
    keyValue = key.call(parent, data[i], i, data) + "";
    if (node = nodeByKeyValue.get(keyValue)) {
      update[i] = node;
      node.__data__ = data[i];
      nodeByKeyValue.delete(keyValue);
    } else {
      enter[i] = new EnterNode(parent, data[i]);
    }
  }

  // Add any remaining nodes that were not bound to data to exit.
  for (i = 0; i < groupLength; ++i) {
    if ((node = group[i]) && (nodeByKeyValue.get(keyValues[i]) === node)) {
      exit[i] = node;
    }
  }
}

function datum(node) {
  return node.__data__;