Postfix to infix conversion using stack in typescript

Ts program for Postfix to infix conversion using stack. Here problem description and other solutions.

// TypeScript program for
// Postfix To Infix Conversion

// Stack Node
class StackNode
{
	public data: string;
	public next: StackNode;
	constructor(data: string, top: StackNode)
	{
		this.data = data;
		this.next = top;
	}
}
class MyStack
{
	public top: StackNode;
	public count: number;
	constructor()
	{
		this.top = null;
		this.count = 0;
	}
	// Returns the number of element in stack
	public number size()
	{
		return this.count;
	}
	public boolean isEmpty()
	{
		if (this.size() > 0)
		{
			return false;
		}
		else
		{
			return true;
		}
	}
	// Add a new element in stack
	public push(data: string)
	{
		// Make a new stack node
		// And set as top
		this.top = new StackNode(data, this.top);
		// Increase node value
		this.count++;
	}
	// Add a top element in stack
	public string pop()
	{
		var temp = "";
		if (this.isEmpty() == false)
		{
			// Get remove top value
			temp = this.top.data;
			this.top = this.top.next;
			// Reduce size
			this.count--;
		}
		return temp;
	}
	// Used to get top element of stack
	public string peek()
	{
		if (!this.isEmpty())
		{
			return this.top.data;
		}
		else
		{
			return "";
		}
	}
}
class Conversion
{
	// Check operator
	public boolean isOperator(text: string)
	{
		if (text == '+' || text == '-' || 
            text == '*' || text == '/' || 
            text == '^' || text == '%')
		{
			return true;
		}
		return false;
	}
	// Check operands
	public boolean isOperands(text: string)
	{
		if ((text >= '0' && text <= '9') || 
            (text >= 'a' && text <= 'z') || 
            (text >= 'A' && text <= 'Z'))
		{
			return true;
		}
		return false;
	}
	// Converting the given postfix expression to 
	// infix expression
	public postfixToInfix(postfix: string)
	{
		// Get the size
		var size = postfix.length;
		// Create stack object
		var s = new MyStack();
		// Some useful variables which is using 
		// of to storing current result
		var auxiliary = "";
		var op1 = "";
		var op2 = "";
		var isValid = true;
		for (var i = 0; i < size && isValid; i++)
		{
			// Check whether given postfix location
			// at [i] is an operator or not
			if (this.isOperator(postfix.charAt(i)))
			{
				// When operator exist
				// Check that two operands exist or not
				if (s.size() > 1)
				{
					op1 = s.pop();
					op2 = s.pop();
					auxiliary = "(" + op2 + postfix.charAt(i) + op1 + ")";
					s.push(auxiliary);
				}
				else
				{
					isValid = false;
				}
			}
			else if (this.isOperands(postfix.charAt(i)))
			{
				// When get valid operands
				auxiliary = "" + postfix.charAt(i);
				s.push(auxiliary);
			}
			else
			{
				// Invalid operands or operator
				isValid = false;
			}
		}
		if (isValid == false)
		{
			// When have something wrong
			console.log("Invalid postfix : " + postfix);
		}
		else
		{
			// Display calculated result
			console.log(" Postfix : " + postfix);
			console.log(" Infix   : " + s.pop());
		}
	}
	public static main(args: string[])
	{
		var task = new Conversion();
		var postfix = "ab+c*ef+g/+";
		task.postfixToInfix(postfix);
		postfix = "abc*de-/+";
		task.postfixToInfix(postfix);
	}
}
Conversion.main([]);
/*
 file : code.ts
 tsc --target es6 code.ts
 node code.js
 */

Output

 Postfix : ab+c*ef+g/+
 Infix   : (((a+b)*c)+((e+f)/g))
 Postfix : abc*de-/+
 Infix   : (a+((b*c)/(d-e)))