Complexity between if-else, switch and regex

Question

I'm going to optimize javascript code in which I seen old code is like below,

var emcont = $('#emcont').val();
numericMatch = emcont.match(/\d/g);
if (numericMatch == null) {
    isValid = false;
    $('#msg_emcont').html(getMessage('msg_emcont')).show();
} else if (emcont.length != 14) {
    isValid = false;
    $('#msg_emcont').html(getMessage('msg_emcont')).show();
} else if (numericMatch.length && numericMatch.length != 10) {
    isValid = false;
    $('#msg_emcont').html(getMessage('msg_emcont')).show();
} else {
    $('#msg_emcont').html('').hide();
}

I going to convert if-else conditions into switch conditions, but the problem in the above code is 2nd condition validation used emcont variable so I can't directly use numericMatch in switch statement. So I decided used emcont variable directly in the switch statement like the below code,

switch(emcont)
    {
        case emcont.match(/\d/g) == null:
            isValid = false;
            $('#msg_emcont').html(getMessage('msg_emcont')).show();
            break;
        case emcont.length != 14:
            isValid = false;
            $('#msg_emcont').html(getMessage('msg_emcont')).show();
            break;
         case emcont.match(/\d/g).length && emcont.match(/\d/g).length != 10:
            isValid = false;
            $('#msg_emcont').html(getMessage('msg_emcont')).show();
            break;
        default:
            $('#msg_emcont').html('').hide();
            break;
    }

In used regex in switch case validation, so i need to know which code better in performance wise.

Answer 1

Please do not abuse side effects of switch(true) which is what you meant

This is DRY and easier to read

var emcont = $('#emcont').val();
const numericMatch = emcont.match(/\d/g);
$('#msg_emcont')
  .html(getMessage('msg_emcont'))
  .toggle(
    numericMatch == null || 
    emcont.length != 14  || 
    (numericMatch.length && numericMatch.length != 10)
  )

You might even consider to move

$('#msg_emcont').html(getMessage('msg_emcont'))

to the page load so it is only done once