.fadeIn()

Display the matched elements by fading them to opaque.

.fadeIn(duration, complete)🡢 jQuery

`duration`	Number, String	Default: `400` A string or number determining how long the animation will run.
`complete`	Function	A function to call once the animation is complete, called once per matched element.

.fadeIn(options)🡢 jQuery


                    options

PlainObject

A map of additional options to pass to the method.

`duration`	Number, String, Boolean, String	Default: `400` A string or number determining how long the animation will run.
`easing`	String	Default: `swing` A string indicating which easing function to use for the transition.
`queue`	Number, String, Boolean, String	Default: `true` A Boolean indicating whether to place the animation in the effects queue. If false, the animation will begin immediately. As of jQuery 1.7, the queue option can also accept a string, in which case the animation is added to the queue represented by that string. When a custom queue name is used the animation does not automatically start; you must call `.dequeue("queuename")` to start it.
`specialEasing`	PlainObject	An object containing one or more of the CSS properties defined by the properties argument and their corresponding easing functions.
`step`	Function	A function to be called for each animated property of each animated element. This function provides an opportunity to modify the Tween object to change the value of the property before it is set.
`progress`	Function	A function to be called after each step of the animation, only once per animated element regardless of the number of animated properties.
`complete`	Function	A function that is called once the animation on an element is complete.
`start`	Function	A function to call when the animation on an element begins.
`done`	Function	A function to be called when the animation on an element completes (its Promise object is resolved).
`fail`	Function	A function to be called when the animation on an element fails to complete (its Promise object is rejected).
`always`	Function	A function to be called when the animation on an element completes or stops without completing (its Promise object is either resolved or rejected).

.fadeIn(duration, easing, complete)🡢 jQuery

`duration`	Number, String	Default: `400` A string or number determining how long the animation will run.
`easing`	String	Default: `swing` A string indicating which easing function to use for the transition.
`complete`	Function	A function to call once the animation is complete, called once per matched element.

The .fadeIn() method animates the opacity of the matched elements. It is similar to the .fadeTo() method but that method does not unhide the element and can specify the final opacity level.

Durations are given in milliseconds; higher values indicate slower animations, not faster ones. The strings 'fast' and 'slow' can be supplied to indicate durations of 200 and 600 milliseconds, respectively. If any other string is supplied, or if the duration parameter is omitted, the default duration of 400 milliseconds is used.

We can animate any element, such as a simple image:

<div id="clickme">
  Click here
</div>
<img id="book" src="book.png" alt="" width="100" height="123">

// With the element initially hidden, we can show it slowly:
$( "#clickme" ).click(function() {
  $( "#book" ).fadeIn( "slow", function() {
    // Animation complete
  });
});

Figure 1 - Illustration of the `fadeIn()` effect

Easing

As of jQuery 1.4.3, an optional string naming an easing function may be used. Easing functions specify the speed at which the animation progresses at different points within the animation. The only easing implementations in the jQuery library are the default, called swing, and one that progresses at a constant pace, called linear. More easing functions are available with the use of plug-ins, most notably the jQuery UI suite.

Callback Function

If supplied, the callback is fired once the animation is complete. This can be useful for stringing different animations together in sequence. The callback is not sent any arguments, but this is set to the DOM element being animated. If multiple elements are animated, it is important to note that the callback is executed once per matched element, not once for the animation as a whole.

As of jQuery 1.6, the .promise() method can be used in conjunction with the deferred.done() method to execute a single callback for the animation as a whole when all matching elements have completed their animations ( See the example for .promise() ).

Animates hidden divs to fade in one by one, completing each animation within 600 milliseconds.

<span>Click here...</span>
<div id="one"></div>
<div id="two"></div>
<div id="three"></div>

CSS

span {
  color: red;
  cursor: pointer;
}
div {
  margin: 3px;
  width: 80px;
  display: none;
  height: 80px;
  float: left;
}
#one {
  background: #f00;
}
#two {
  background: #0f0;
}
#three {
  background: #00f;
}

HTML

$(document.body).click(function () {
  $("div:hidden").first().fadeIn("slow");
});

DEMO

Fades a red block in over the text. Once the animation is done, it quickly fades in more text on top.

<p>
  Let it be known that the party of the first part
  and the party of the second part are henceforth
  and hereto directed to assess the allegations
  for factual correctness... (<a href="#">click!</a>)
  <div><span>CENSORED!</span></div>
</p>

CSS

p {
  position: relative;
  width: 400px;
  height: 90px;
}
div {
  position: absolute;
  width: 400px;
  height: 65px;
  font-size: 36px;
  text-align: center;
  color: yellow;
  background: red;
  padding-top: 25px;
  top: 0;
  left: 0;
  display: none;
}
span {
  display: none;
}