brainfuck in typescript

brainfuck.ts

declare function require(module:string):any;
declare var process:any;

var readline = require('readline');
var fs = require('fs');

type brainfuckDone = (char : string) => void;
type brainfuckInput = (done : brainfuckDone) => void;

function brainfuck(tokens : string[], inp : brainfuckInput) {
	var heap = [0];
	var pointer = 0;
	var idx = 0;

	function movePointer(diff : number) {
		pointer += diff;

		if (typeof heap[pointer] === 'undefined') {
			heap[pointer] = 0;
		}
	}

	function forwardTo(char : string, recurseString : string) {
		let count = 0;
		for (idx = idx + 1; idx < tokens.length; idx++) {
			let token = tokens[idx];

			if (token === recurseString) {
				count++;
			} else if (token === char) {
				if (count === 0) {
					break;
				} else {
					count--;
				}
			}
		}
	}

	function backTo(char : string, recurseString : string) {
		let count = 0;
		for (idx = idx - 1; idx > 0; idx--) {
			let token = tokens[idx];

			if (token === recurseString) {
				count++;
			} else if (token === char) {
				if (count === 0) {
					break;
				} else {
					count--;
				}
			}
		}
	}

	function next() {
		if (idx < tokens.length) {
			idx++;
			handleToken();
		}
	}

	function handleToken() {
		let token = tokens[idx];
		let shouldNext = true;

		switch (token) {
			case '+':
				heap[pointer]++;
			break;

			case '-':
				heap[pointer]--;
			break;

			case '>':
				movePointer(1);
			break;

			case '<':
				movePointer(-1);
			break;

			case '[':
				if (heap[pointer] === 0) {
					forwardTo(']', '[');
				}
			break;

			case ']':
				if (heap[pointer] !== 0) {
					backTo('[', ']');
				}
			break;

			case '.':
				fs.writeSync(process.stdout.fd, String.fromCharCode(heap[pointer]));
			break;

			case ',':
				inp(str => {
					heap[pointer] = str.charCodeAt(0);
					next();	
				});

				shouldNext = false;
			break;
		}

		if (shouldNext) {
			next();
		}
	}

	handleToken();
}

brainfuck(`
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++.
+++++++++++++++++++++++++++++.
+++++++.
.
+++.
-------------------------------------------------------------------.
------------.
+++++++++++++++++++++++++++++++++++++++++++++++++++++++.
++++++++++++++++++++++++.
+++.
------.
--------.
-------------------------------------------------------------------.
`.split(''), (done : brainfuckDone) => {
	var rl = readline.createInterface({
	  input: process.stdin,
	  output: process.stdout
	});

	rl.question("Input [Only One Char] ", function(answer) {
	  rl.close();

	  done(answer[0]);
	});
});