indexOf 实现

/* indexOf 实现 */
function index(string, subString, startPos) {
  var i = startPos;
  var j = 0;
  var lenOfString = string.length;
  var lenOfSubString = subString.length;
  while (i < lenOfString && j < lenOfSubString) {
    if (string[i] == subString[j]) {
      i++;
      j++;
    } else {
      i = i - j + 1;
      j = 0;
    }
  }
  if (j == lenOfSubString) {
    return i - lenOfSubString;
  } else {
    return -1;
  }
}
var i = index("1111你好", "你", 4);
console.log(i);