1. /** @module stance/utils */
2.  
3. define('stance/utils',[
4.     'exports',
5.  
6.     'core/utils/lang/isElement',
7.     'core/utils/uniqueId',
8. ], function (
9.     exports,
10.  
11.     isElement,
12.     uniqueId
13. ) {
14.     'use strict';
15.  
16.     /**
17.      * Extracts element from container if applicable.
18.      *
19.      * @param {Element-like} obj
20.      * @returns {?HTMLElement}
21.      */
22.     exports.getElement = function (obj) {
23.         if (isElement(obj))
24.             return obj;
25.  
26.         return obj && obj.el;
27.     };
28.  
29.     exports.EL_ID_ATTR = 'data-visibility-id';
30.     exports.OBJ_ID_PROP = '_visibility_id';
31.  
32.     /**
33.      * Get or create an id for the element or element container, or return null.
34.      *
35.      * @param {Element-like} obj
36.      * @returns {?number} Id of the associated element / view
37.      */
38.     exports.getId = function (obj) {
39.         // Gets the id (possibly creating it)
40.         var id = null;
41.  
42.         // TODO: Refactor
43.         if (isElement(obj)) {
44.             // Store the id as an element attribute
45.             id = obj.getAttribute(exports.EL_ID_ATTR) || null;
46.  
47.             if (!id) {
48.                 id = uniqueId();
49.                 obj.setAttribute(exports.EL_ID_ATTR, id);
50.             }
51.         } else if (obj) {
52.             // Store it as a property
53.             id = obj[exports.OBJ_ID_PROP] || null;
54.  
55.             if (!id)
56.                 id = obj[exports.OBJ_ID_PROP] = uniqueId();
57.         }
58.         return id;
59.     };
60.  
61.     /**
62.      * Calculate the the percentage of an element visible in
63.      * the viewport given the scroll position and the element's offset.
64.      *
65.      * @param {ViewportPos} pos - Scroll information.
66.      * @param {FullOffset} offset - Element's full offset information.
67.      * @returns {Integer} Percent between 0 and 100
68.      */
69.     exports.visiblePercent = function (pos, offset) {
70.         var percent = 0;
71.  
72.         if (!offset)
73.             return percent;
74.  
75.         var screenTop = pos.top;
76.         var screenBottom = screenTop + pos.height;
77.  
78.         var bleedsTop = offset.visibleTop < screenTop;
79.         var bleedsBottom = offset.visibleBottom > screenBottom;
80.  
81.         // If the view bleeds over the top and bottom of the viewport then it
82.         // is filling the entire viewport, so report 100%. Otherwise, if it
83.         // bleeds over neither, then it is completely in view, so also report 100%.
84.         if ((!bleedsTop && !bleedsBottom) || (bleedsTop && bleedsBottom))
85.             percent = 1;
86.         // If the view is bleeding off the top, the calculate how much of the bottom of the view is visible.
87.         else if (bleedsTop)
88.             percent = (offset.height - (screenTop - offset.visibleTop)) / offset.height;
89.         // Otherwise, if bleeding off the bottom, then calculate how much of the top of the view is visible.
90.         else if (bleedsBottom)
91.             percent = (screenBottom - offset.visibleTop) / offset.height;
92.  
93.         return Math.round(percent * 100);
94.     };
95.  
96. });
97.  
98.   // https://c.disquscdn.com/next/next-core/core/stance/utils.js
99.