JS: Add hyphens as you type

hyphens.js

 function mask(str, textbox, loc, delim) {
		    var locs = loc.split(',');

		    for (var i = 0; i <= locs.length; i++) {
		      for (var k = 0; k <= str.length; k++) {
		        if (k == locs[i]) {
		            if (str.substring(k, k + 1) != delim) {
		                str = str.substring(0, k) + delim + str.substring(k, str.length)
		            }
		        }
		      }
		    }
		    textbox.value = str
		  }

$('#key').on({
	keyup: function(){
		cachedThis = $(this);
		cachedThis.val(cachedThis.val().replace(/[^0-9]/g, ''));
		return mask(this.value,this,'3,7','-');

	},
	blur: function(){
		return mask(this.value,this,'3,7','-');
	}
})