Get first postcode part from UK postcode with vanilla javascript

gistfile1.txt

function postcodePart($postcode) { //https://www.mrs.org.uk/pdf/postcodeformat.pdf
	var $postcodePart;
	switch($postcode.length) {
	    case 5:
	        $postcodePart = $postcode.substr(0,2)
	        break;
	    case 6:
	        $postcodePart = $postcode.substr(0,3)
	        break;
	    case 7:
	    	$postcodePart = $postcode.substr(0,4)
	        break;
	    default:
	    	$postcodePart = $postcode;
	    	break;
	}
	return $postcodePart;
}

gistfile2.txt

function postcodePart($postcode) { //https://www.mrs.org.uk/pdf/postcodeformat.pdf
	var $postcodePart;
	switch($postcode.length) {
	    case 5:
	        $postcodePart = $postcode.substr(0,2)
	        break;
	    case 6:
	        $postcodePart = $postcode.substr(0,3)
	        break;
	    case 7:
	    	$postcodePart = $postcode.substr(0,4)
	        break;
	    default:
	    	$postcodePart = $postcode;
	    	break;
	}
	return $postcodePart;
}