how to get previous checked checkbox value and compare to newly checked box

[thetylercox]

i am trying to create a checkbox limit based on a value changes!

 

If the value of a checked checked box is different then the previous prompt an alert! Some of the check boxes do have the same value. Not all of them!

 

example: I have the following checkbox!

<input name="" type="checkbox" value="here">(if this was checked)
<input name="" type="checkbox" value="here">(then this)
<input name="" type="checkbox" value="there">(would not allow prompt alert) 
<input name="" type="checkbox" value="here">(would allow)

 

my problem is in the if statement

 

function setChecks(obj){d=document.getElementByclass(chk) If(d.value!=d.value) {obj.checked=false alert('you may only choose options from the same dist!') }

 

something like this obviously this will not work but its where im at! So How do i store the previous checked checkbox value and compare it to the just checked box!