我的搜索功能不起作用

Question

 var cat = prompt("What Do You Want To Tweet??!");

 if(cat.length >= 140)
 {
 confirm("Sorry but your Tweet was over the 140 character limit by: " + (cat.length - 140));
 confirm("You need to resubmit a Tweet that is not over the 140 Character limit");
 }
 else{
confirm("Success, Your Tweet has been posted!");
 }
 //scan for websites

 if (cat.search(" www ", " http ", ".com"))
 {

 }
 else{
 confirm("We have Detected a URL in your Tweet");   
 }

---

我的代码一直工作，直到我尝试“推特”一个网站。如果我输入www或.com作为推文，它会告诉我它已检测到一个好的网址。但当我输入xxxxxx www xxxxxx（x为anythingelse）时，它不会检测到网址