Minimum Add to Make Parentheses Valid.js

// Runtime: 81 ms (Top 66.54%) | Memory: 42.2 MB (Top 75.00%)
var minAddToMakeValid = function(s) {
    let stack = []
    let count = 0
    for(let i=0;i<s.length;i++) {
        let ch = s[i]
        if(ch === '(') {
            stack.push(ch)
        } else {
            let top = stack.pop()
            if(top != '(') count++
        }
    }

    count += stack.length

    return count
};