Abstract Syntax Tree (JavaScript)

ast.js

var Node = (function(){
	return function _Node(operation, value, leftChild, rightChild){
		this.operation = operation;
		this.value = value;
		this.leftChild = leftChild;
		this.rightChild = rightChild;
	};
}());

function evaluate(node){
	if(node.value !== null){
		return node.value;
    	}
	
	switch(node.operation){
		case "+": return evaluate(node.leftChild) + evaluate(node.rightChild);
		case "-": return evaluate(node.leftChild) - evaluate(node.rightChild);
		case "*": return evaluate(node.leftChild) * evaluate(node.rightChild);
		case "/": return evaluate(node.leftChild) / evaluate(node.rightChild);
     	}
	
	return 0;
}

main.js

//Eval 5 + ( 25 * 6 )

/*
      +
     / \
    *   5
   / \
  25  6

*/

// Create Nodes
var sixNode = new Node(null, 6, null, null);
var fiveNode = new Node(null, 5, null, null);
var twentyFiveNode = new Node(null, 25, null, null);

var mult25_6Node = new Node("*", null, twentyFiveNode, sixNode);
var rootPlusNode = new Node("+", null, mult25_6Node, fiveNode);

// Usage
evaluate(rootPlusNode); // -> 155