Implement the Equals Operation

equals() {
  const { previous, current, operation } = this.state;

  if (previous === null || operation === null) {
    return Number(current);
  }

  try {
    const result = this.perform(previous, current, operation);

    this.state.current = String(result);
    this.state.lastExpression = `${previous} ${operation} ${current}`;
    this.state.previous = null;
    this.state.operation = null;
    this.state.waitingForOperand = true;
    this.state.justCalculated = true;

    return result;
  } catch (error) {
    this.state.current = 'Error';
    this.state.previous = null;
    this.state.operation = null;
    this.state.waitingForOperand = true;
    this.state.justCalculated = true;

    throw error;
  }
}

if (action === 'operation') {
  calculator.chooseOperation(button.dataset.value);
}

if (action === 'equals') {
  try {
    calculator.equals();
  } catch (error) {
    console.error(error);
  }
}

updateDisplay();