Question

Here i have an array with undefined number of elements. I tried to print random element of this array and cut it. Here my code.

function rand(min, max){
   return (Math.floor(Math.random() * (max - min + 1)) + min).toFixed(0);
}
$('#do').click(function(){
    var count = chamarr.length;
    var num = 0;
    if (count == 1) {
      $('#output').html('Nothing can found');
    } else {
      num = rand(1,chamarr.length);
      $('#output').html(chamarr[num]);
      chamarr.splice(num,1);
    }
 });

When I logged an array is cutted, I saw that always ok, but sometimes element is not cut!

Answer 1

My guess is that the problem is with your randnum method:

function rand(min, max){
   return (Math.floor(Math.random() * (max - min + 1)) + min).toFixed(0);
}

I believe this will give you a value in the range [min, max] – inclusive at both ends. (Well, actually, it will give you a string version of that value as toFixed returns a string, but when you use it later it’ll get coerced back into a number.)

Now you’re calling it like this:

num = rand(1,chamarr.length);

So if the array is 6 elements long, you’ll get a value in the range [1, 6]. But then you’ll try to take chamarr[num] – and the range of valid indexes is [0, 5] as arrays are 0-based. If you try to take element 6, that will give you undefined – but then splicing at element 6 won’t do anything.

I would change your rand method to be exclusive at the upper bound, like this:

function rand(min, max) {
   return (Math.floor(Math.random() * (max - min)) + min).toFixed(0);
}

and then call it like this:

num = rand(0, chamarr.length);

That will give you a value in the right range for both indexing and splicing.

EDIT: In response to comments etc:

• It’s probably worth removing the toFixed(0) part of the rand function; you don’t really want a string, after all. This isn’t really part of what was wrong before, but it’s generally cleaner:

  function rand(min, max) {
     return Math.floor(Math.random() * (max - min)) + min;
  }
  

• You might also want a version of the function that makes the 0 lower bound implicit

• If you’re not going to use random numbers anywhere else in your code you could inline the Math.floor() / Math.random() calls instead of having a separate function, but personally I’d want to keep them well away from the “logic” code which just wants to get a random number and use it.
• The reason I’d change the function is that having an exclusive upper bound is much more common in computer science – it typically goes along with 0-indexing for things like collections. You typically write for loops with inclusive lower bounds and exclusive lower bounds, etc.