问从头开始构建JavaScript计算器？

EN

function newNum(pressed) { //Adds digit of key pressed to new number being entered.
  //console.log ("Button pressed " + pressed);

  if (newValue == 0) { //If new calculation, newValue is set to key pressed.
    newValue += pressed;
  } else { //Else if continuing calculation, key pressed is added to end of newValue.
    newValue = newValue.toString();
    newValue = newValue + pressed; //Adds digit at end of String, then converts back to Number.
    newValue = parseFloat(newValue);
  }
  document.getElementById('result').innerHTML = newValue;
}

function newCalc(pressed) { //Will use this mathematical operation to find the value.
  if (!currentValue) {
    currentValue = newValue;
  } else {
    document.getElementById('result').innerHTML = newValue;
  }

  newOperation = pressed;
  newValue = 0;
}

function equals() { //Resolves calculation.
  newValue = parseFloat(newValue);

  switch(newOperation) {
    case "/":
        currentValue = (currentValue / newValue);
        break;
    case "*":
        currentValue = (currentValue * newValue);
        break;
    case "-":
        currentValue = (currentValue - newValue);
        break;
    case "+":
        currentValue = (currentValue + newValue);
        break;
  }

  currentValue = parseFloat(currentValue);
  newValue = 0;
  document.getElementById('result').innerHTML = currentValue;
}