parse str.js

//It works only with + and - operation
//If need to use operations like * or / and so on: need to add prioriry of operations
//Also exist algoritm with "stack" and "recursion".
//Current algoritm is most simple way for equialent operations.

var str = "1-(2-3-(4-5))+6-(8-10)+(3+4)";

function _calculate(a, op, b) {
    a = a * 1;
    b = b * 1;
    switch (op) {
        case '+':
            return a + b;
        case '-':
            return a - b;
    }
}

function calculateStr(input) {
    input = input.replace(/^[^0-9]|\\-|\\+|\(|\)/g, ''); // clean up unnecessary characters
    var output;
    //Parse by one
    var re = new RegExp('(\\d+\\.?\\d*)([\+\-])(\\d+\\.?\\d*)');
    // execute all
    while (re.test(input)) {
        output = _calculate(RegExp.$1, RegExp.$2, RegExp.$3);
        if (isNaN(output) || !isFinite(output)) {
            return output; // exit early if not a number
        }

        input = input.replace(re, output);
    }

    return output;
}
console.info(str);
console.info(calculateStr(str));
console.info('Check:');
console.info(eval(str));