A small question about JavaScript, can someone see what the problem is?

Recently learning JavaScript, there is a very strange problem, first put out the code:

functionBinarySearch () {vararr = [0,1,2,3]; varres = Actbinarysearch (0,3,2, arr); document.write ("<br/>return is" +res);}functionActbinarysearch (Left,right,val,arr) {if(Left >Right ) {document.write ("Do not find"); return-1; }    varMidindex = Math.floor ((left+right)/2);varMidval =Arr[midindex]; if(Val <midval) {Actbinarysearch (left, Midindex-1, Val,arr); }Else if(Val >midval) {Actbinarysearch (Midindex+1, right, Val, arr); }Else{document.write ("Find it" +Midindex); returnMidindex; }}

The simple dichotomy, but the result is very strange, the result is as follows:

Do not know why inconsistent, very confusing, to you to consult.

A small question about JavaScript, can someone see what the problem is?