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The ngShow directive shows or hides the given HTML element based on the expression provided to the ngShow attribute. The element is shown or hidden by removing or adding the .ng-hide CSS class onto the element. The .ng-hide CSS class is predefined in AngularJS and sets the display style to none (using an !important flag). For CSP mode please add angular-csp.css to your html file (see ngCsp).

<!-- when $scope.myValue is truthy (element is visible) -->
<div ng-show="myValue"></div>

<!-- when $scope.myValue is falsy (element is hidden) -->
<div ng-show="myValue" class="ng-hide"></div>

When the ngShow expression evaluates to a falsy value then the .ng-hide CSS class is added to the class attribute on the element causing it to become hidden. When truthy, the .ng-hide CSS class is removed from the element causing the element not to appear hidden.

Why is !important used?

You may be wondering why !important is used for the .ng-hide CSS class. This is because the .ng-hide selector can be easily overridden by heavier selectors. For example, something as simple as changing the display style on a HTML list item would make hidden elements appear visible. This also becomes a bigger issue when dealing with CSS frameworks.

By using !important, the show and hide behavior will work as expected despite any clash between CSS selector specificity (when !important isn't used with any conflicting styles). If a developer chooses to override the styling to change how to hide an element then it is just a matter of using !important in their own CSS code.

Overriding .ng-hide

By default, the .ng-hide class will style the element with display: none!important. If you wish to change the hide behavior with ngShow/ngHide then this can be achieved by restating the styles for the .ng-hide class CSS. Note that the selector that needs to be used is actually .ng-hide:not(.ng-hide-animate) to cope with extra animation classes that can be added.

.ng-hide:not(.ng-hide-animate) {
  /* this is just another form of hiding an element */
  display: block!important;
  position: absolute;
  top: -9999px;
  left: -9999px;
}

By default you don't need to override in CSS anything and the animations will work around the display style.

A note about animations with ngShow

Animations in ngShow/ngHide work with the show and hide events that are triggered when the directive expression is true and false. This system works like the animation system present with ngClass except that you must also include the !important flag to override the display property so that you can perform an animation when the element is hidden during the time of the animation.

//
//a working example can be found at the bottom of this page
//
.my-element.ng-hide-add, .my-element.ng-hide-remove {
  /* this is required as of 1.3x to properly
     apply all styling in a show/hide animation */
  transition: 0s linear all;
}

.my-element.ng-hide-add-active,
.my-element.ng-hide-remove-active {
  /* the transition is defined in the active class */
  transition: 1s linear all;
}

.my-element.ng-hide-add { ... }
.my-element.ng-hide-add.ng-hide-add-active { ... }
.my-element.ng-hide-remove { ... }
.my-element.ng-hide-remove.ng-hide-remove-active { ... }

Keep in mind that, as of AngularJS version 1.3.0-beta.11, there is no need to change the display property to block during animation states--ngAnimate will handle the style toggling automatically for you.