Reverse polish notation algorithm

reversePolish.js

/**
Author's note: This is the algorithm taken from https://en.wikipedia.org/wiki/Reverse_Polish_notation

for each token in the postfix expression:
  if token is an operator:
    operand_2 ← pop from the stack
    operand_1 ← pop from the stack
    result ← evaluate token with operand_1 and operand_2
    push result back onto the stack
  else if token is an operand:
    push token onto the stack
result ← pop from the stack

*/

function calculate(expression) {
  if (expression === '') {
    return '';
  }

  const stack = [];
  const tokens = expression.split(' ');
  const operators = ['+', '-', '*', '/'];

  tokens.forEach((t, i) => {
    const operator = operators.find((o) => o === t);

    if (operator) {
      const first = stack.pop();
      const second = stack.pop();

      const result = `${second} ${operator} ${first}`;
      stack.push(eval(result));
    } else {
      stack.push(t);
    }
  });

  return stack.pop();
}