jQuery - How to find out if part of a variable is in an array

I want it so that when the user types in their postcodes it sees if we support their area. I have completed this but instead of having thousands of possible postcodes I have just put in part of the postcode into the array. This is what I have so far:

<script>
var zips = ['CM14','CM11','CM12','CM13','SS16','SS15','CM1','CM2','CM4','SS12','SS13','SS14','CM15','SS11'];
var bad = ['CM16','CM17','CM18','CM19','CM20','CM21','CM23','CM24','CM25','CM26','CM2','CM28','CM29'];
$(function(){
  $('input[name=zip]').on( 'blur' , function(){
    var currentVal = $(this).val();
    var res = currentVal.toUpperCase();
    if($.inArray(res, bad)> -1){
    $('.checkout_button').prop('disabled',true);
     alert("if")
    } else if($.inArray(res, zips)> -1){
     alert("else if")
     $('.checkout_button').prop('disabled',false);
    } else {
     alert("else")
     $('.checkout_button').prop('disabled',true);
      }
    });
});
</script> 

This above works but I want it so that if the user typed in SS12 7HF then it would return else if because SS12 is part of SS12 7HF. How would I complete this?