回调函数不返回任何内容

Question

var res = "";
function longest(sen, callback) {
  sen = sen.split(" ");
  for(var i = 0; i < sen.length; i++) {
    callback(sen[i]);
  }
}

function findLongest(item) {
  if(item.length > res.length) {
    res = item;
  }
  return res;
}

longest("the greatest day EVERERAWEREWRWRAEWR",findLongest);

I'm trying to find the longest word in the string I input, but all it does is return undefined. I know there's a lot of easier ways to find the longest word, but I want to do it implementing a callback like such.

Answer 1

longest updates res (via the callback) but does not return anything. Try printing out res after your call to longest , or returning res from longest .

Answer 2

 var res = ""; function longest(sen, callback) { sen = sen.split(" "); for(var i = 0; i < sen.length; i++) { callback(sen[i]); } } function findLongest(item) { if(item.length > res.length) { res = item; console.log('now max len is %s',item); } } longest("the greatest day EVERERAWEREWRWRAEWR",findLongest); 

remove return,since you don't use it. replace with console.log so you can see result.