How to replace work item type value with a different value

Hi,
I would like to replace the "Type: Task" to "Type:TSK" in my email template subject. This is my idea below:
<script>
function myFunction() {
    var task = "TSK";
    var Defect= "DFT";
}
</script>
#if(${workItem.type} == "Task") myFunction(Defect) #end

My main goal is to make my work item type an abbreviation on my subject content. I also tried the following below but i got an error message:
Type:          ${workItem.type.abbreviation}

any responses would be helpful. Thanks