simple JavaScript math-based CAPTCHA

math-captcha.js

// This script should be loaded or embedded after the form.
// There must be an element with an ID of "answer" and a form with an ID of "myform".
// Beginners: you can change what IDs the script looks for by replacing all instances of #answer or #myform

function set_question(){
  operation = Math.floor( Math.random() * 2 ); // 1 or 0
  constant1 = Math.floor( Math.random() * 11 ); // 0 through 10
  constant2 = Math.floor( Math.random() * 11 ); // 0 through 10
  if( operation == 1 ){
    operation_symbol = "+";
    answer = constant1 + constant2;
  } else if( operation == 0 ){
    operation_symbol = "–";
    answer = constant1 - constant2;
  }
  $("#problem").remove();
  $("#answer").before('<strong id="problem">' + constant1 + ' ' + operation_symbol + ' ' + constant2 + '<br></strong>');
};
set_question();

$("#myform").submit(function(){
  if( $('#answer').attr('value') == answer){
    return true;
  } else {
    alert('Verification answer incorrect. Please try again.');
    $('#answer').focus().attr('value','');
    set_question();
    return false;
  }
});

This CAPTCHA is only designed to guard against simple garden-variety spam bots and will not likely hold up against high-grade spam bots. No guarantees are made that this script will prevent automated form submission. I am testing it to see how it holds up. Kinda new to the spam-fighting game. Suggestions are welcome.