const calculator = { displayValue: "0", firstOperand: null, waitingForSecondOperand: false, operator: null, }; function inputDigit(digit) { const { displayValue, waitingForSecondOperand } = calculator; if (waitingForSecondOperand === true) { calculator.displayValue = digit; calculator.waitingForSecondOperand = false; } else { calculator.displayValue = displayValue === "0" ? digit : displayValue + digit; } } function inputDecimal(dot) { if (calculator.waitingForSecondOperand === true) return; // If the `displayValue` does not contain a decimal point if (!calculator.displayValue.includes(dot)) { // Append the decimal point calculator.displayValue += dot; } } function handleOperator(nextOperator) { const { firstOperand, displayValue, operator } = calculator; const inputValue = parseFloat(displayValue); if (operator && calculator.waitingForSecondOperand) { calculator.operator = nextOperator; r...