✏️ Editing: appear.js Writable

/*
 * jQuery.appear
 * https://github.com/bas2k/jquery.appear/
 * http://code.google.com/p/jquery-appear/
 * http://bas2k.ru/
 *
 * Copyright (c) 2009 Michael Hixson
 * Copyright (c) 2012-2014 Alexander Brovikov
 * Licensed under the MIT license (http://www.opensource.org/licenses/mit-license.php)
 */
(function($) {
    $.fn.appear = function(fn, options) {

var settings = $.extend({

//arbitrary data to pass to fn
            data: undefined,

//call fn only on the first appear?
            one: true,

// X & Y accuracy
            accX: 0,
            accY: 0

}, options);

return this.each(function() {

var t = $(this);

//whether the element is currently visible
            t.appeared = false;

if (!fn) {

//trigger the custom event
                t.trigger('appear', settings.data);
                return;
            }

var w = $(window);

//fires the appear event when appropriate
            var check = function() {

//is the element hidden?
                if (!t.is(':visible')) {

//it became hidden
                    t.appeared = false;
                    return;
                }

//is the element inside the visible window?
                var a = w.scrollLeft();
                var b = w.scrollTop();
                var o = t.offset();
                var x = o.left;
                var y = o.top;

var ax = settings.accX;
                var ay = settings.accY;
                var th = t.height();
                var wh = w.height();
                var tw = t.width();
                var ww = w.width();

if (y + th + ay >= b &&
                    y <= b + wh + ay &&
                    x + tw + ax >= a &&
                    x <= a + ww + ax) {

//trigger the custom event
                    if (!t.appeared) t.trigger('appear', settings.data);

} else {

//it scrolled out of view
                    t.appeared = false;
                }
            };

//create a modified fn with some additional logic
            var modifiedFn = function() {

//mark the element as visible
                t.appeared = true;

//is this supposed to happen only once?
                if (settings.one) {

//remove the check
                    w.unbind('scroll', check);
                    var i = $.inArray(check, $.fn.appear.checks);
                    if (i >= 0) $.fn.appear.checks.splice(i, 1);
                }

//trigger the original fn
                fn.apply(this, arguments);
            };

//bind the modified fn to the element
            if (settings.one) t.one('appear', settings.data, modifiedFn);
            else t.bind('appear', settings.data, modifiedFn);

//check whenever the window scrolls
            w.scroll(check);

//check whenever the dom changes
            $.fn.appear.checks.push(check);

//check now
            (check)();
        });
    };

//keep a queue of appearance checks
    $.extend($.fn.appear, {

checks: [],
        timeout: null,

//process the queue
        checkAll: function() {
            var length = $.fn.appear.checks.length;
            if (length > 0) {
                while (length--) {
                    if ( $.isFunction($.fn.appear.checks[length]) ) {
                        $.fn.appear.checks[length]();
                    }
                };
            };
        },

//check the queue asynchronously
        run: function() {
            if ($.fn.appear.timeout) clearTimeout($.fn.appear.timeout);
            $.fn.appear.timeout = setTimeout($.fn.appear.checkAll, 20);
        }
    });

//run checks when these methods are called
    $.each(['append', 'prepend', 'after', 'before', 'attr',
        'removeAttr', 'addClass', 'removeClass', 'toggleClass',
        'remove', 'css', 'show', 'hide'], function(i, n) {
        var old = $.fn[n];
        if (old) {
            $.fn[n] = function() {
                var r = old.apply(this, arguments);
                $.fn.appear.run();
                return r;
            }
        }
    });

})(jQuery);

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