String to Integer - Javascript

This function is not for converting character string : ASCII to integer.
Check this blog for ASCII to integer in C++ -
http://www.muktadadariya.com/2016/11/string-to-interger-write-your-own-atoi-c.html

function stoi(string) {
var i = 0
var number = 0
var flag = 0
var stringlength = string.length

if (string[0] == '-') {
flag = 1
i++
}

while (i < stringlength) {
//number *= 10
number = number * 10
//number += string[i]-'0'
number = number + (string[i]-'0')
i++
}

if (flag == 1) {
//number *= -1
number = number * -1
}
return number
}
console.log(stoi("-57"))