Simple javascript calculator if statement

Question

I'm a newbie in JS but I have tried to create an 'if' statement in my calculator, which creates an alert when the result of a multiplication or an addition, etc. is bigger than 20. The calculator works fine but the 'if' statement doesn't.

JS:

var a,b;
function setValues()
{
    a = Number(document.getElementById("a").value);
    b = Number(document.getElementById("b").value);
}

function sum()
{
    setValues();
    result = a+b;
    alert("the sum is equal to "+result);
}
function rest()
{
    setValues();
    result = a-b;
    alert("the rest is equal to "+result);
}
function mult()
{
    setValues();
    result = a*b;
    alert("the operation is equal to "+result);
}
function div()
{
    setValues();
    result = a/b;
    alert("the operation is equal to "+result);
}

if (result > 20) {
    alert("heyy thats pretty big"); 
}

Answer 1

Your if statement should be inside each operator function like so:

function div()
{
  setValues();
  result = a/b;
  alert("the operation is equal to "+result);
  checkResult(result);
}

function checkResult(result){
  if(result > 20)
    alert("heyy thats pretty big");
}

Answer 2

Ask yourself when that 'if' will be executed. It's not inside any of the functions, so how will it be called? I cannot tell without seeing the whole page, but it looks like it will only be executed at the time the page is loaded.