04. Jan's Notation

function janNotation(input) {
    for (let i = 0; i < input.length; i++) {
        let [firstOperand, secondOperand, operator] = input.slice(i, i + 3);
        if (typeof (firstOperand + secondOperand) === 'number') {
            if (typeof (operator) === 'string') {
                operator === '+' ? firstOperand += secondOperand :
                    operator === '-' ? firstOperand -= secondOperand :
                        operator === '*' ? firstOperand *= secondOperand :
                            firstOperand /= secondOperand;
                input.splice(i, 3, firstOperand);
                i = -1;
            }
        } else {
            return console.log('Error: not enough operands!');
        }
    }
    console.log(input.length === 1 ? input[0] : 'Error: too many operands!');
}