JS expression eval tree

var str = "1+2.2*3.3";
var numbers = str.match(/(\d+(?:\.\d+)?)/g);
var signs = str.match(/[+\-*\/]/g);
var priorities = {"+": 1, "-": 1, "*": 2, "/": 2};
console.log(numbers);
console.log(signs);

var EvalTree = function() {
    this.left  = null;
    this.right = null;
    this.value = null;
    this.add   = function(operandL, operandR, sign) {
        this.
    }
};

var parseTree = new EvalTree();

var num = 0;
priorities.sort(function(a, b) {
    return b[1] - a[1];
});
for(var i in signs) {
    if(signs[i] in prorities) {