Postfix calculator

postfixcalc.js

function Stack() {
  let arr = []
  return {
    push: (data) => arr.push(data),
    pop: () => arr.pop(),
    show: () => arr
  }
}

function calc(string, showstack) {
  let stack = Stack()
  let inputs = string.split(" ")

  inputs.forEach(char => {
    if (!["+","-","*","/","%"].includes(char)) {
      stack.push(char)
      if (showstack) console.log(stack.show())
    } else {
      const value1 = stack.pop()
      const value2 = stack.pop()
      const expr =  value2 + char + value1
      const value = eval(expr)
      stack.push(value)
      if (showstack) console.log(stack.show())
    }
  })
  return stack.pop()
}


calc("3 4 + 5 2 / *", true)
calc("3 4 - 5 2 / *")
calc("11 5 %")
calc("2 2 * 2 2 * *")