Attach an Opacity effect

The Opacity effect makes the target element disappear or appear by changing the CSS opacity property. The Fade effect uses the Opacity effect.

You can attach the Fade effect to any HTML element except applet, body, iframe, object, tr, tbody, or th.

To link the SpryEffects.js file on your web page, add the following code to the head of your document:
```
<head>
. . .
<script  src="../includes/SpryEffects.js" type="text/javascript" ></script>
</head>
```
Note: The exact file path differs, depending on where you store the SpryEffects.js file.

The SpryEffects.js file is in the includes folder of the Spry folder that you downloaded from Adobe Labs. See Prepare your files.

Make sure your target element has a unique ID. The target element is the element that changes when the user interacts with the page to cause the effect.

<div id="opacity1"><p>Lorem ipsum dolor sit amet, consetetur 
sadipscing elitr, sed diam nonumy eirmod tempor invidunt ut 
labore et dolore magna aliqt</p></div>

To create the effect, add a JavaScript event to trigger the effect, and a script tag that creates the effect object. For example, if you want the user to click on a sentence that causes another paragraph to disappear by changing opacity, you might add the following event and script tag:
```
<p><a onclick="opacity_effect.start(); return false;" href="#">Click here to hide the paragraph.</a></p>
. . .
<script type="text/javascript">
var opacity_effect = new Spry.Effect.Opacity("opacity1", 1, 0.1, {duration: 2000});
</script>
```
Note: It’s important that you add the script tag after the code for the target element. Otherwise the page will return a JavaScript error when you try to trigger the effect.

The first argument of the Spry.Effect.Opacity method is always the target element’s ID ("opacity1" in the preceding example).

The second and the third arguments are the starting and ending opacity values. These values should be numbers between 0 and 1, where 0 makes the element invisible and 1 makes the element completely visible.

The complete code looks as follows:
```
<head>
. . .
<script src="../includes/SpryEffects.js" type="text/javascript"></script>
</head>
<body>
<p><a onclick="opacity_effect.start(); return false;" href="#">Click here to hide the paragraph.</a></p>
<div id="opacity1"><p>Lorem ipsum dolor sit amet, consetetur 
sadipscing elitr, sed diam nonumy eirmod tempor invidunt ut 
labore et dolore magna aliqt</p></div>
<script type="text/javascript">
var opacity_effect = new Spry.Effect.Opacity("opacity1", 1, 0.1, {duration: 2000});
</script>
</body>
```

Opacity effect options

The following table lists available options for the Opacity effect.

Option	Description
duration	Duration of the effect in milliseconds. The default value is 1000.
toggle	Lets you create a toggle effect. The default value is `false`.
transition	Determines the type of transition. The default is `Spry.sinusoidalTransition`.
fps	Determines the number of frames per second (fps) of the animation. The default is 60.
setup	Lets you define a function that is called before the effect begins, e.g.,`setup:function (element,effect){/* ... */}`.
finish	Lets you define a function that is called after the effect finishes, e.g., `finish:function (element,effect){/* ... */}`.

Sample code:

var effect = new Spry.Effect.Opacity("targetID", 1, 0.5, {duration: 2000, toggle: true});

effect.start();