Basic Calculator II
var calculate = function(s) {
s += '+'
let wait = []
let num = 0
let sign = '+'
for (var i = 0; i < s.length; i++) {
if (s[i] === ' ') continue
if (!isNaN(s[i])) num = 10 * num + Number(s[i])
else {
if (sign === "+") {
wait.push(num)
} else if (sign === "-") {
wait.push(-num)
} else if (sign === "*") {
wait.push(wait.pop() * num)
} else {
wait.push(Math.trunc(wait.pop() / num))
}
sign = s[i]
num = 0
}
}
return wait.reduce((a,b)=>a+b)
}