Log a binary tree data structure to the console

log-binary-tree.js

/**
 * Recursively print a binary tree data structure
 * @param {function} printFn            function used to print output; called with a single string argument
 * @param {object} node                 current node object
 * @param {string|function} leftKey     name of current node's left child property, or a function that accepts the
 *                                        current node and returns the left child node
 * @param {string|function} rightKey    name of current node's right child property, or a function that accepts the
 *                                        current node and returns the right child node
 * @param {string|function} displayKey  property to display, or a function that returns a display string
 * @param {string} [indent='']          current indentation string; mostly used to build up indentation across levels
 *                                        of recursion, but may be used to provide a prefix for all printed lines
 */
function printNode(printFn, node, leftKey, rightKey, displayKey, indent) {
  // default to empty string to avoid logging the word 'undefined'
  indent = indent || '';
  
  // current item's indentation prefix
  var prefix = indent+'\\-';
  
  var leftChild  = leftKey.constructor  === Function ? leftKey(node)  : node[leftKey],
      rightChild = rightKey.constructor === Function ? rightKey(node) : node[rightKey];
  
  var displayStr = displayKey.constructor === Function ? displayKey(node) : node[displayKey];
  printFn(prefix+' '+displayStr);
  
  // recurse left
  if (!!leftChild) printNode(printFn, leftChild, leftKey, rightKey, displayKey, indent+(!!rightChild?' |':'  '));
  // recurse right
  if (!!rightChild) printNode(printFn, rightChild, leftKey, rightKey, displayKey, indent+'  ');
}

/** Wrapper around {link:printNode} that always uses console.log() as the print function **/
var logNode = printNode.bind(null, console.log.bind(console));


/*  Sample output from a simple Rope tree structure implementation holding the string "The quick brown fox jumps over the lazy dog.":

> logNode(rope.root, node=>rope.nodes[node.left], node=>rope.nodes[node.right], node=>(node.leaf ? '"'+node.value+'"' : node.weight))

\- 32
| \- 16
|  |\- 8
|  | |\- 4
|  | | |\- "The "
|  | |  \- "quic"
|  |  \- 4
|  |   |\- "k br"
|  |    \- "own "
|   \- 8
|    |\- 4
|    | |\- "fox "
|    |  \- "jump"
|     \- 4
|      |\- "s ov"
|       \- "er t"
 \- 12
   \- 8
    |\- 4
    | |\- "he l"
    |  \- "azy "
     \- 4
       \- "dog."
*/