如何判断字符串包含某个子串

String.prototype.includes();

String.prototype.IndexOf = function (searchValue, fromIndex) {
  const string = this;
  const len = string.length;
 
  // 默认值为 0
  let n = fromIndex | 0;
  // 如果 fromIndex 的值小于 0，或者大于 str.length ，那么查找分别从 0 和str.length 开始
  let k = n <= 0 ? 0 : n >= len ? len : n;
  while (k < len) {
    const subStr = string.substring(k, k + searchValue.length);
    if (subStr === searchValue) {
      return k;
    }
    k++;
  }
  return -1;
};
 
console.log("hello world".IndexOf("ll") + "/" + "hello world".indexOf("ll"));
console.log(
  "hello world".IndexOf("ll", -1) + "/" + "hello world".indexOf("ll", -1),
);
console.log(
  "hello world".IndexOf("or", -6) + "/" + "hello world".indexOf("or", -6),
);
console.log(
  "hello world".IndexOf("wo", 12) + "/" + "hello world".indexOf("wo", 12),
);