AI solution for JavaScript Coding Question on BFE.dev
124. calculate arithmetic expression

One possible solution is:

/**
 * @param {string} str
 * @return {number}
 */
function calculate(str) {
  const tokens = tokenize(str);

  function parseExpr() {
    let left = parseTerm();
    while (tokens.length > 0 && (tokens[0] === '+' || tokens[0] === '-')) {
      const op = tokens.shift();
      const right = parseTerm();
      if (op === '+') {
        left += right;
      } else {
        left -= right;
      }
    }
    return left;
  }

  function parseTerm() {
    let left = parseFactor();
    while (tokens.length > 0 && (tokens[0] === '*' || tokens[0] === '/')) {
      const op = tokens.shift();
      const right = parseFactor();
      if (op === '*') {
        left *= right;
      } else {
        left /= right;
      }
    }
    return left;
  }

  function parseFactor() {
    if (tokens[0] === '(') {
      tokens.shift(); // consume '('
      const value = parseExpr();
      tokens.shift(); // consume ')'
      return value;
    } else {
      return Number(tokens.shift());
    }
  }

  // start parsing from the expression level
  return parseExpr();
}

The calculate function first tokenizes the input string using the tokenize function from the previous question. Then it defines three helper functions: parseExpr for parsing addition and subtraction expressions, parseTerm for parsing multiplication and division expressions, and parseFactor for parsing numbers and parentheses.

Each function uses a recursive descent parsing technique, meaning that it calls other functions to parse sub-expressions when needed. The parsing order is determined by operator precedence and associativity rules, which are encoded in the function structure.

The result of the calculate function is the value of the top-level expression, which is obtained by calling parseExpr.