jansNotation

function myFunc(inputArr) {
    const resultingArr = [];
    const operators = {
        "*": (n1, n2) => n1 * n2,
        "/": (n1, n2) => n1 / n2,
        "+": (n1, n2) => n1 + n2,
        "-": (n1, n2) => n1 - n2,
    };

    while (inputArr.length > 0) {
        let sign = inputArr.shift();
        if (!operators.hasOwnProperty(sign)) {
            resultingArr.push(sign);
            continue;
        }
        let num2 = resultingArr.pop();
        let num1 = resultingArr.pop();
        if (num1 == undefined || num2 == undefined) {
            console.log("Error: not enough operands!");
            return;
        }
        resultingArr.push(operators[sign](num1, num2));
    }
    if (resultingArr.length > 1) {
        console.log("Error: too many operands!");
        return;
    }
    console.log(resultingArr[0]);
}

myFunc([15, "/"]);