freeCodeCamp/guide/english/miscellaneous/guide-to-build-a-sliding-image-gallery/index.md

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Guide to Build a Sliding Image Gallery

This tutorial will walk you through building an image slider using the jQuery library.

This tutorial will have four parts:

• HTML
• SCSS
• JS
• References

HTML

We will be using Bootstrap for this tutorial to keep things looking good, without spending a lot of time.

Our structure will be as follows:

<div class="container">

  <!-- The wrapper for our slider -->
  <div class="slider">
    <ul class="slides"><!-- Each image will be inside this unordered list --></ul>
  </div>

  <div class="buttons"><!-- Pause and play buttons will go in here --></div>

</div>

Inside our ul with the class of slides we will have the following:

<li class="slide"><img src="#" /></li>
<li class="slide"><img src="#" /></li>
<li class="slide"><img src="#" /></li>
<li class="slide"><img src="#" /></li>
<li class="slide"><img src="#" /></li>

Inside our .buttons class you should have the following:

<button type="button" class="btn btn-default pause">
	<span class="glyphicon glyphicon-pause"></span>
</button>
<button type="button" class="btn btn-default play">
	<span class="glyphicon glyphicon-play"></span>
</button>

Here is an example of what your html should look like:

Note: You should replace the image src attribute with your own content.

<div class="container">

  <div class="slider">
    <ul class="slides">
      <li class="slide"><img src="https://unsplash.it/1280/720/?image=120" /></li>
      <li class="slide"><img src="https://unsplash.it/1280/720/?image=70" /></li>
      <li class="slide"><img src="https://unsplash.it/1280/720/?image=50" /></li>
      <li class="slide"><img src="https://unsplash.it/1280/720/?image=170" /></li>
      <li class="slide"><img src="https://unsplash.it/1280/720/?image=190" /></li>
    </ul>
  </div>

  <div class="buttons">
    <button type="button" class="btn btn-default pause">
      <span class="glyphicon glyphicon-pause"></span>
    </button>
    <button type="button" class="btn btn-default play">
      <span class="glyphicon glyphicon-play"></span>
    </button>
  </div>

</div>

SCSS

We are using Sass and the SCSS syntax so we can nest and use variables

We can use the following SCSS to define our styling:

// Variables
$width: 720px;

.slider {
  width: $width;
  height: 400px;
  overflow: hidden;
  margin: 0 auto;
  text-align: center;

  .slides {
    display: block;
    width: 6000px;
    height: 400px;
    margin: 0;
    padding: 0;
  }

  .slide {
    float: left;
    list-style-type: none;
    width: $width;
    height: 400px;

    img {
      width: 100%;
      height: 100%;
    }
  }
}

.buttons {
  margin: 0;
  width: $width;
  position: relative;
  top: -40px;
  margin: 0 auto;

  .play {
    display: none;
  }

  .btn {
    display: flex;
    margin: 0 auto;
    text-align: center;
  }
}

JS

Variables

In the following code snippet, we define variables used later in our code.

var animationSpeed = 1000; // How quickly the next slide animates.
var pause = 3000; // The pause between each slide.

We will use a blank variable where we will call the setInterval method:

var interval;

Animation We will wrap our slider animations inside a function:

function startSlider() {}

We are using the setInterval() native JavaScript method to automate the contents of the function on a time based trigger.

interval = setInterval(function() {}, pause);

We use the pause variable to see how many milliseconds to wait before calling the function again. Read more on the native setInterval method here: https://developer.mozilla.org/en-US/docs/Web/API/WindowTimers/setInterval. Inside our function we will use jQuery to fade between slides at the speed of the animationSpeed variable:

$('.slides > li:first')
  .fadeOut(animationSpeed)
  .next()
  .fadeIn(animationSpeed)
  .end()
  .appendTo('.slides');

• We are targeting the first slide using $('.slides > li:first'). - .fadeOut(animationSpeed) will fade the first slide out and then using .next(), we move to the next slide. - Once we have moved to the next slide, we will fade it in: .fadeIn(animationSpeed). - This sequence will continue until the last slide (.end()), then we stop the animation. We will now call the startSlider function to start the animation:

  startSlider();

Play and Pause This feature is optional, but quite easy to implement. We will hide the play button, so we don't see both the play and pause buttons:

$('.play').hide(); // Hiding the play button.

We will now create our pause button (automatically shown on page load):

$('.pause').click(function() {
	clearInterval(interval);
	$(this).hide();
	$('.play').show();
});

• We will call our function every time the pause button is clicked using jQuery. - We will remove the interval using the clearInterval method and using our interval variable as the parameter, indicating which interval to stop. - Because our slider is paused, we will hide the pause button using $(this).hide();. Note: we are using this, which will refer to what our parent is calling i.e. .pause. - We will then show our play button so the user can resume the animation: $('.play').show();. The following code sets up our play button (automatically hidden on page load):

  $('.play').click(function() { startSlider(); $(this).hide(); $('.pause').show(); });

• We will call our function every time the play button is clicked using jQuery.
  • We will start or restart the interval using the startSlider function.
  • Because our slider is currently playing, we will hide the play button using $(this).hide();. Note: we are using this, which will refer to what our parent is calling i.e. .play.
  • We will then show our pause button so the user can stop the animation at will: $('.pause').show();.

References

• Checkout the source code and example on CodePen for this tutorial.