Add plugin

Author: frontid

isInViewport.jquery.js

@@ -0,0 +1,67 @@
+/* ====================================================
+ * jQuery Is In Viewport.
+ * https://github.com/frontid/jQueryIsInViewport
+ * Marcelo Iván Tosco (capynet)
+ * Inspired on https://stackoverflow.com/a/40658647/1413049
+ * ==================================================== */
+!function ($) {
+  'use strict'
+
+  var plugin
+
+  var Class = function (el, cb) {
+    plugin = this
+    this.$el = $(el)
+    this.cb = cb
+    watch()
+    return this
+  }
+
+  /**
+   * Checks if the element is in.
+   *
+   * @returns {boolean}
+   */
+  function isIn () {
+    var $win = $(window)
+    var elementTop = plugin.$el.offset().top
+    var elementBottom = elementTop + plugin.$el.outerHeight()
+    var viewportTop = $win.scrollTop()
+    var viewportBottom = viewportTop + $win.height()
+    return elementBottom > viewportTop && elementTop < viewportBottom
+  }
+
+  /**
+   * Launch a callback indicating when the element is in and when is out.
+   */
+  function watch () {
+    var _isIn = false
+
+    $(window).on('resize scroll', function () {
+
+      if (isIn() && _isIn === false) {
+        plugin.cb('entered')
+        _isIn = true
+      }
+
+      if (_isIn === true && !isIn()) {
+        plugin.cb('leaved')
+        _isIn = false
+      }
+
+    })
+  }
+
+  // jQuery plugin.
+  //-----------------------------------------------------------
+  $.fn.isInViewport = function (cb) {
+    return this.each(function () {
+      var $element = $(this)
+      var data = $element.data('isInViewport')
+      if (!data) {
+        $element.data('isInViewport', (new Class(this, cb)))
+      }
+    })
+  }
+
+}(window.jQuery)