实现strStr()

实现strStr()

strStr(haystack, needle){
      if(!needle)
        return 0;
      let count = 0;
      for(let i=0; i<haystack.length; i++){
        if(haystack.charAt(i) === needle.charAt(count)){
          if(haystack.substring(i, i+needle.length) === needle){
            return i;
          }
          continue;
        }
      }
      return -1;
    },