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# `ngHide`
directive in module `ng`

## Description

The `ngHide` directive shows and hides the given HTML element conditionally based on the expression provided to the ngHide attribute. The show and hide mechanism is a achieved by removing and adding the `ng-hide` CSS class onto the element. The `.ng-hide` CSS class is a predefined CSS class present in AngularJS which sets the display style to none (using an !important flag).

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

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

When the ngHide expression evaluates to true then the .ng-hide CSS class is added to the class attribute on the element causing it to become hidden. When false, 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

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 in CSS:

    .ng-hide {

    display:block!important;

      //this is just another form of hiding an element
      position:absolute;
      top:-9999px;
      left:-9999px;
    }

Just remember to include the important flag so the CSS override will function.

## A note about animations with ngHide

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 similar to the animation system present with ngClass, however, the only difference is 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 {
      transition:0.5s linear all;
      display:block!important;
    }

    .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 { ... }

## Usage

as attribute

    <ANY ng-hide="{expression}">
       ...
    </ANY>

as class

    <ANY class="ng-hide: {expression};">
       ...
    </ANY>

### Animations

- removeClass: .ng-hide - happens after the ngHide expression evaluates to a truthy value and just before the contents are set to hidden
- addClass: .ng-hide - happens after the ngHide expression evaluates to a non truthy value and just before the contents are set to visible

Click here to learn more about the steps involved in the animation.

#### Parameters

Param | Type | Details
--- | --- | ---
ngHide | expression | If the expression is truthy then the element is shown or hidden respectively.

## Example

#### Source

## Demo