String To Integer

 1 var myAtoi = function(str) {
 2     var res = 0,
 3         i = 0,
 4         isNegtive = false,
 5         isFirst = true;
 6 
 7 
 8     for (i = 0; i < str.length; i++) {
 9         if (isFirst && str[i] === ' ') {
10             continue;
11         } else if (isFirst && (str[i] === '-' || str[i] === '+')) {
12             isNegtive = str[i] === '-' ? true : false;
13             isFirst = false;
14         } else if (str[i] >= '0' && str[i] <= '9') {
15             res = res * 10 + (str[i] - '0');
16             isFirst = false;
17         } else {
18             break;
19         }
20     }
21 
22     res = isNegtive ? -res : res;
23 
24     if (res > 2147483647) {
25         res = 2147483647;
26     } else if (res < -2147483648) {
27         res = -2147483648;
28     }
29 
30     return res;
31 };
32 
33 console.log(myAtoi("  -0012a42"));