Binary Search Tree Syntax

Question

For this portion of an implementation of a binary search tree in JS, what is the significance of referring to "this._root"? (why can't they say "this.root")? The link for this is available at http://www.nczonline.net/blog/2009/06/16/computer-science-in-javascript-binary-search-tree-part-2/

BinarySearchTree.prototype = {

    //more code here

    remove: function(value){

        var found       = false,
            parent      = null,
            current     = this._root,
            childCount,
            replacement,
            replacementParent;

        //make sure there's a node to search
        while(!found && current){

            //if the value is less than the current node's, go left
            if (value < current.value){
                parent = current;
                current = current.left;

            //if the value is greater than the current node's, go right
            } else if (value > current.value){
                parent = current;
                current = current.right;

            //values are equal, found it!
            } else {
                found = true;
            }
        }

        //only proceed if the node was found
        if (found){
            //continue
        }

    },

    //more code here

};

Answer 1

They may be trying to indicate that this variable should not be accessed outside of the object ( private in other languages).

Python has a strong convention of using names starting with underscore character to indicate that this field or method is private. The author may be trying to apply the same convention to javascript.

Answer 2

I suppose that more complete example is located here: https://github.com/nzakas/computer-science-in-javascript/blob/master/data-structures/binary-search-tree/binary-search-tree.js

Regarding this._root - I think it's author's decision only, without any special meaning.