Auto Show Hide DIV Javascript syntax

Question

One little doubt in javascript accept this code

$('#B').css("display", "none" : "block");

if div B is display: none on event auto switch to block

Answer 1

On init you could check using jQuery's :hidden selector

// App init:
$('#B:visible').hide();

than if you need to .toggle() it on some event:

// Some event:
$('#B').toggle();

Example:

$("[data-toggle]").on("click", function() {
  $(this.dataset.toggle).toggle();
});

<button data-toggle="#B" type="button">Toggle B</button>
<div id="B">Lorem ut florem</div>

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>

A preferred way, instead of using jQuery's show/hide/toggle methods is to use .toggleClass() and define in CSS the needed styles

$("[data-toggle]").on("click", function() {
  $(this.dataset.toggle).toggleClass("is-hidden");
});

/* Bool helpers */
.is-hidden { display:none; }

<button data-toggle="#B" type="button">Toggle B</button>
<div id="B" class="is-hidden">Lorem ut florem</div>

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>