function Node(value){
this.value = value;
this.left = null;
this.right = null;
}
var a = new Node('a');
var b = new Node('b');
var c = new Node('c');
var d = new Node('d');
var e = new Node('e');
var f = new Node('f');
var g = new Node('g');
a.left = c;
a.right = b;
c.left = f;
c.right = g;
b.left = d;
b.right = e;
function f1(node){
if( node == null) return;
console.log(node.value)
f1(node.left)
f1(node.right)
}
f1(a)
function f2(){
if( node == null) return;
f2(node.left)
console.log(node.value)
f2(node.right)
}
f2(a)
function f3(){
if( node == null) return;
f3(node.left)
f3(node.right)
console.log(node.value)
}
f3(a)