1var assert = require('assert');
2
3function calculator(str) {
4  let result = 0,
5    sign = 1;
6  const stack = [],
7    operationStack = [];
8
9  for (let i = 0; i < str.length; i++) {
10    const curr = str.charAt(i);
11    if (curr === ' ') {
12      continue;
13    } else if (curr === '+') {
14      sign = 1;
15    } else if (curr === '-') {
16      sign = -1;
17    } else if (curr >= '0' && curr <= '9') {
18      let num = curr;
19      while (
20        i + 1 < str.length &&
21        str.charAt(i + 1) >= '0' &&
22        str.charAt(i + 1) <= '9'
23      ) {
24        num += str.charAt(i + 1);
25        i++;
26      }
27      result += sign * parseInt(num);
28    } else if (curr === '(') {
29      stack.push(result);
30      result = 0;
31      operationStack.push(sign);
32      sign = 1;
33    } else if (curr === ')') {
34      result = operationStack.pop() * result + stack.pop();
35      sign = 1;
36    }
37  }
38  return result;
39}
40
41try {
42  assert.equal(calculator('2 + 2'), 4);
43
44  console.log('PASSED: ' + "assert.equal(calculator('2 + 2'), 4)");
45} catch (err) {
46  console.log(err);
47}
48
49try {
50  assert.equal(calculator('(2+2) - 3'), 1);
51
52  console.log('PASSED: ' + "assert.equal(calculator('(2+2) - 3'), 1)");
53} catch (err) {
54  console.log(err);
55}