javascript - indexOf is not a funciton -

i have event...

   <textarea id="chat"> </textarea>    <button type="button" onclick="play_song();">talk</button> 

... triggering following function:

   var input = function() {            var chat = document.getelementbyid("chat").value.split(" ");            return chat && console.log(chat);         } 

then there's function:

   function setintersection(a, b) {        var result = [];        (var = 0; < a.length; i++) {          if (b.indexof(a[i]) !== -1 && result.indexof(a[i]) === -1) {             result.push(a[i]);          }       }     return result;    } 

a prototype function:

   song.prototype.lyricsintersect = function(input) {         var bestsong = null;       var bestcount = -infinity;        (var in songs) {         var currentcount = setintersection(songs[i].lyrics, input).length;      if (currentcount > bestcount) {         bestsong = songs[i];         bestcount = currentcount;     } }  return bestsong && bestsong.name; } 

the code ends here:

   function play_song() {      var id = song.prototype.lyricsintersect(input);     var element = document.getelementbyid(id);     element.play(); } 

but console.log returns: uncaught typeerror: b.indexof not function

if test var input = ["one", "two"];, however, intersection done on code depending on input.

what missing?

var currentcount = setintersection(songs[i].lyrics, input).length; 

should be

var currentcount = setintersection(songs[i].lyrics, input()).length; 

this relies on input being corrected follows

var input = function() {    var chat = document.getelementbyid("chat").value.split(" ");    return chat; }