Tokenize and convert a math expression from infix to postfix in Javascript

rpn-parser.js

function parse(inp){
	var outQueue=[];
	var opStack=[];

	Array.prototype.peek = function() {
		return this.slice(-1)[0];
	};

	var assoc = {
		"^" : "right",
		"*" : "left",
		"/" : "left",
		"+" : "left",
		"-" : "left"
	};

	var prec = {
		"^" : 4,
		"*" : 3,
		"/" : 3,
		"+" : 2,
		"-" : 2
	};

	Token.prototype.precedence = function() {
		return prec[this.value];
	};
	
	Token.prototype.associativity = function() {
		return assoc[this.value];
	};

	//tokenize
	var tokens=tokenize(inp);

	tokens.forEach(function(v) {
		//If the token is a number, then push it to the output queue
		if(v.type === "Literal" || v.type === "Variable" ) {
			outQueue.push(v);
		} 
		//If the token is a function token, then push it onto the stack.
		else if(v.type === "Function") {
			opStack.push(v);
		} //If the token is a function argument separator 
		else if(v.type === "Function Argument Separator") {
			//Until the token at the top of the stack is a left parenthesis
			//pop operators off the stack onto the output queue.
			while(opStack.peek()
				&& opStack.peek().type !== "Left Parenthesis") {
				outQueue.push(opStack.pop());
		}
			/*if(opStack.length == 0){
				console.log("Mismatched parentheses");
				return;
			}*/
		} 
		//If the token is an operator, o1, then:
		else if(v.type == "Operator") {
			  //while there is an operator token o2, at the top of the operator stack and either
			  while (opStack.peek() && (opStack.peek().type === "Operator") 
				//o1 is left-associative and its precedence is less than or equal to that of o2, or
				&& ((v.associativity() === "left" && v.precedence() <= opStack.peek().precedence())
					//o1 is right associative, and has precedence less than that of o2,
					|| (v.associativity() === "right" && v.precedence() < opStack.peek().precedence()))) {
			  	outQueue.push(opStack.pop());
			}
			//at the end of iteration push o1 onto the operator stack
			opStack.push(v);
		} 
		
		//If the token is a left parenthesis (i.e. "("), then push it onto the stack.
		else if(v.type === "Left Parenthesis") {
			opStack.push(v);
		}
		//If the token is a right parenthesis (i.e. ")"):
		else if(v.type === "Right Parenthesis") {
			//Until the token at the top of the stack is a left parenthesis, pop operators off the stack onto the output queue.
			while(opStack.peek() 
				&& opStack.peek().type !== "Left Parenthesis") {
				outQueue.push(opStack.pop());
		}
			/*if(opStack.length == 0){
				console.log("Unmatched parentheses");
				return;
			}*/
			//Pop the left parenthesis from the stack, but not onto the output queue.
			opStack.pop();

			//If the token at the top of the stack is a function token, pop it onto the output queue.
			if(opStack.peek() && opStack.peek().type === "Function") {
				outQueue.push(opStack.pop());
			}
		}
	});

	return outQueue.concat(opStack.reverse());
}

function toString(rpn) {
	return rpn.map(token => token.value).join(" ");
}

Note that the code in this file needs the code in tokenizer.js to work.

Hi and thank You. Unfortunately this won't work with unary '-' - try to convert -5 * 3 for example...