String To Integer

var myAtoi = function(str) {
    var res = 0,
        i = 0,
        isNegtive = false,
        isFirst = true;


    for (i = 0; i < str.length; i++) {
        if (isFirst && str[i] === ' ') {
            continue;
        } else if (isFirst && (str[i] === '-' || str[i] === '+')) {
            isNegtive = str[i] === '-' ? true : false;
            isFirst = false;
        } else if (str[i] >= '0' && str[i] <= '9') {
            res = res * 10 + (str[i] - '0');
            isFirst = false;
        } else {
            break;
        }
    }

    res = isNegtive ? -res : res;

    if (res > 2147483647) {
        res = 2147483647;
    } else if (res < -2147483648) {
        res = -2147483648;
    }

    return res;
};

console.log(myAtoi("  -0012a42"));