diff --git a/solutions/javascript/binary-search-tree.js b/solutions/javascript/binary-search-tree.js
index 6f5e74d..645b39f 100644
--- a/solutions/javascript/binary-search-tree.js
+++ b/solutions/javascript/binary-search-tree.js
@@ -1,37 +1,107 @@
 var root,
   createNode,
-  add;
+  add,
+  search,
+  addSubNode,
+  findRightMost,
+  replaceNodeInParent,
+  binaryTreeDelete; // not overwrite keyword.
 
 createNode = function createNode(num) {
   return {
     add: add,
+    search: search,
+    delete: binaryTreeDelete,
     left: undefined,
     right: undefined,
     value: num
   };
 };
 
-add = function add(num) {
+addSubNode = function(node, direct, num) {
+  if (node[direct] === undefined) {
+    node[direct] = createNode(num);
+  } else {
+    node[direct].add(num);
+  }
+};
+
+add = function(num) {
+  // Add the value to the correct side of the binary search tree. 
+  // If the value is the same as the current node, we'll just ignore it.
   if (this.value === undefined) {
     this.value = num;
   } else {
     if (num < this.value) {
-      if (this.left === undefined) {
-        this.left = createNode(num);
-      } else {
-        this.left.add(num);
-      }
+      addSubNode(this, 'left', num);
     } else if (num > this.value) {
-      if (this.right === undefined) {
-        this.right = createNode(num);
-      } else {
-        this.right.add(num);
-      }
+      addSubNode(this, 'right', num);
+    }
+  }
+  return root;
+};
+
+search = function(num) {
+  if (num === this.value) {
+    return this;
+  } else if (num < this.value && this.left) {
+    return this.left.search(num);
+  } else if (num > this.value && this.right) {
+    return this.right.search(num);
+  } else {
+    return false;
+  }
+};
+
+findRightMost = function(node) {
+  if (node.right === undefined) {
+    return node;
+  }
+  return findRightMost(node.right);
+};
+
+replaceNodeInParent = function(node, parent, newNode) {
+  // root's parent is undefined.
+  if (parent === undefined) {
+    if (newNode) {
+      root.value = newNode.value,
+      root.left = newNode.left,
+      root.right = newNode.right;
+    }else{
+      root.value=undefined;
+    }
+    return;
+  }
+
+  if (parent.left === node) {
+    parent.left = newNode;
+  } else {
+    parent.right = newNode;
+  }
+};
+
+
+binaryTreeDelete = function(num, parent) {
+  var successor;
+  if (num < this.value) {
+    return this.left ? this.left.delete(num, this) : root;
+  } else if (num > this.value) {
+    return this.right ? this.right.delete(num, this) : root;
+  } else {
+    // delete key here
+    if (this.left !== undefined && this.right !== undefined) {
+      successor = findRightMost(this.left);
+      this.value = successor.value;
+      this.left.delete(successor.value, this);
+    } else if (this.left) {
+      replaceNodeInParent(this, parent, this.left);
+    } else if (this.right) {
+      replaceNodeInParent(this, parent, this.right);
     } else {
-      return false;
+      replaceNodeInParent(this, parent); // replace with undefined
     }
   }
   return root;
 };
 
-module.exports = (root = createNode(undefined));
+module.exports = (root = createNode(undefined));
\ No newline at end of file
diff --git a/tests/javascript/binary-search-tree.js b/tests/javascript/binary-search-tree.js
new file mode 100644
index 0000000..2599baf
--- /dev/null
+++ b/tests/javascript/binary-search-tree.js
@@ -0,0 +1,113 @@
+var assert = require('assert');
+var isBST = require('../../solutions/javascript/binary-search-tree-check');
+var bst = require('../../solutions/javascript/binary-search-tree');
+
+var root = bst.add(50).add(9).add(100)
+  .add(7).add(10).add(8).add(6)
+  .add(75).add(150).add(175).add(125);
+
+var node = function(value, left, right) {
+  var result = {
+    value: value
+  };
+  if (left) {
+    result.left = left;
+  }
+  if (right) {
+    result.right = right;
+  }
+  return result;
+};
+
+var jsonify = function(object) {
+  return JSON.parse(JSON.stringify(object));
+};
+
+var expect;
+
+describe('binary search tree', function() {
+  it('root should pass a valid binary search tree', function() {
+    expect = node(50,
+      node(9,
+        node(7, node(6), node(8)),
+        node(10)
+      ),
+      node(100,
+        node(75),
+        node(150, node(125), node(175))
+      )
+    );
+
+    assert.ok(isBST(root));
+    assert.deepEqual(jsonify(root), jsonify(expect));
+  });
+
+  it('deleting nodes should pass a valid binary search tree', function() {
+    root.delete(125).delete(9).delete(75);
+
+    expect = node(50,
+      node(8,
+        node(7, node(6)),
+        node(10)
+      ),
+      node(100,
+        undefined,
+        node(150, undefined, node(175))
+      )
+    );
+    assert.ok(isBST(root));
+    assert.deepEqual(jsonify(root), jsonify(expect));
+  });
+
+  it('deleting unexisted nodes should pass a valid binary search tree',
+    function() {
+      root.delete(1252222).delete(20392); //delete unexisted node 
+      assert.ok(isBST(root));
+      assert.deepEqual(jsonify(root), jsonify(expect));
+    });
+
+  it('search nodes', function() {
+    var searchExpect;
+    var searchResult = root.search(999999); // if not existed
+    assert.ok(!searchResult);
+
+    searchResult = root.search(125);
+    assert.ok(!searchResult);
+
+    searchExpect = node(7, node(6));
+    searchResult = root.search(7); // if existed
+    assert.deepEqual(jsonify(searchResult), jsonify(searchExpect));
+
+    searchExpect = node(100, undefined, node(150, undefined, node(175)));
+    searchResult = root.search(100); // if existed
+    assert.deepEqual(jsonify(searchResult), jsonify(searchExpect));
+
+    searchExpect = node(50, node(8, node(7, node(6)), node(10)),
+      node(100, undefined, node(150, undefined, node(175))));
+    searchResult = root.search(50); // if existed
+    assert.deepEqual(jsonify(searchResult), jsonify(searchExpect));
+  });
+
+  it('delete root', function() {
+    var rootExpect;
+
+    root.delete(50);
+    rootExpect = node(10, node(8, node(7, node(6))),
+      node(100, undefined, node(150, undefined, node(175))));
+    assert.deepEqual(jsonify(root), jsonify(rootExpect));
+
+    //remove left sub tree
+    root.delete(10).delete(8).delete(7).delete(6);
+    rootExpect = node(100, undefined, node(150, undefined, node(175)));
+    assert.deepEqual(jsonify(root), jsonify(rootExpect));
+
+    //remove right sub tree
+    root.delete(175).delete(150).add(6).add(5).add(8).add(7).delete(100);
+    rootExpect = node(6, node(5), node(8, node(7)));
+    assert.deepEqual(jsonify(root), jsonify(rootExpect));
+
+    //remove every node.
+    root.delete(6).delete(5).delete(8).delete(7);
+    assert.equal(undefined, root.value);
+  });
+});
\ No newline at end of file