function calc(left, right, rule) {
switch (rule){
case '+':
return left + right;
case '-':
return left - right;
case '*':
return left * right;
case '/':
return left / right;
}
}
function calcExpress(arr) {
const stack = [];
for(let e of arr) {
if('+-*/'.includes(e)) {
const right = stack.pop();
const left = stack.pop();
const res = calc(left, right, e);
stack.push(res);
}else {
stack.push(e);
}
}
return stack.pop();
}
const arr = [1, 3, '+', 4, '*', 5, '-']
const res = calcExpress(arr);
console.log(res)