js图片预加载记录demo示例（整理）-阿里云开发者社区

js图片预加载记录demo示例（整理）

2023-09-15 71

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简介： js图片预加载记录demo示例（整理）

<!DOCTYPE html>
<html>
<head>
  <meta charset="UTF-8">
   <title>图片预加载记录</title>
</head>
<style type="text/css">
  .box{width: 1000px;height: 7000px;position: relative;}
  .igm1,.igm2,.igm3{width: 1000px;height: 1000px;margin-bottom: 500px;}
</style>
<script src="http://libs.baidu.com/jquery/1.11.1/jquery.min.js"></script>
<body>
<div class="box">
  <!--data-original是要加载的图片 src中的是加载动画-->
  <img class="igm1" data-original='bg.jpg' src=""/>
  <img class="igm2" data-original='bg.jpg' src=""/>
  <img class="igm2" data-original='bg.jpg' src=""/>
</div>
<script type="text/javascript" src="jquery.lazyload.js"></script>
<script type="text/javascript">
$("img").lazyload({
     effect :"fadeIn",
      threshold :200
});
</script>
</body>
</html>
<!-- js引入文件开始 -->
(function($, window, document, undefined) {
    var $window = $(window);
    $.fn.lazyload = function(options) {
        var elements = this;
        var $container;
        var settings = {
            threshold       : 0,
            failure_limit   : 0,
            event           : "scroll",
            effect          : "show",
            container       : window,
            data_attribute  : "original",
            skip_invisible  : false,
            appear          : null,
            load            : null,
            placeholder     : "data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAYAAAAfFcSJAAAAAXNSR0IArs4c6QAAAARnQU1BAACxjwv8YQUAAAAJcEhZcwAADsQAAA7EAZUrDhsAAAANSURBVBhXYzh8+PB/AAffA0nNPuCLAAAAAElFTkSuQmCC"
        };
        function update() {
            var counter = 0;
            elements.each(function() {
                var $this = $(this);
                if (settings.skip_invisible && !$this.is(":visible")) {
                    return;
                }
                if ($.abovethetop(this, settings) ||
                    $.leftofbegin(this, settings)) {
                        /* Nothing. */
                } else if (!$.belowthefold(this, settings) &&
                    !$.rightoffold(this, settings)) {
                        $this.trigger("appear");
                        /* if we found an image we'll load, reset the counter */
                        counter = 0;
                } else {
                    if (++counter > settings.failure_limit) {
                        return false;
                    }
                }
            });
        }
        if(options) {
            if (undefined !== options.failurelimit) {
                options.failure_limit = options.failurelimit;
                delete options.failurelimit;
            }
            if (undefined !== options.effectspeed) {
                options.effect_speed = options.effectspeed;
                delete options.effectspeed;
            }
            $.extend(settings, options);
        }
        $container = (settings.container === undefined ||
                      settings.container === window) ? $window : $(settings.container);
        if (0 === settings.event.indexOf("scroll")) {
            $container.on(settings.event, function() {
                return update();
            });
        }
        this.each(function() {
            var self = this;
            var $self = $(self);
            self.loaded = false;
            if ($self.attr("src") === undefined || $self.attr("src") === false) {
                if ($self.is("img")) {
                    $self.attr("src", settings.placeholder);
                }
            }
            $self.one("appear", function() {
                if (!this.loaded) {
                    if (settings.appear) {
                        var elements_left = elements.length;
                        settings.appear.call(self, elements_left, settings);
                    }
                    $("<img />")
                        .one("load", function() {
                            var original = $self.attr("data-" + settings.data_attribute);
                            $self.hide();
                            if ($self.is("img")) {
                                $self.attr("src", original);
                            } else {
                                $self.css("background-image", "url('" + original + "')");
                            }
                            $self[settings.effect](settings.effect_speed);
                            self.loaded = true;
                            var temp = $.grep(elements, function(element) {
                                return !element.loaded;
                            });
                            elements = $(temp);
                            if (settings.load) {
                                var elements_left = elements.length;
                                settings.load.call(self, elements_left, settings);
                            }
                        })
                        .attr("src", $self.attr("data-" + settings.data_attribute));
                }
            });
            if (0 !== settings.event.indexOf("scroll")) {
                $self.on(settings.event, function() {
                    if (!self.loaded) {
                        $self.trigger("appear");
                    }
                });
            }
        });
        $window.on("resize", function() {
            update();
        });
        if ((/(?:iphone|ipod|ipad).*os 5/gi).test(navigator.appVersion)) {
            $window.on("pageshow", function(event) {
                if (event.originalEvent && event.originalEvent.persisted) {
                    elements.each(function() {
                        $(this).trigger("appear");
                    });
                }
            });
        }
        $(document).ready(function() {
            update();
        });
        return this;
    };
    $.belowthefold = function(element, settings) {
        var fold;
        if (settings.container === undefined || settings.container === window) {
            fold = (window.innerHeight ? window.innerHeight : $window.height()) + $window.scrollTop();
        } else {
            fold = $(settings.container).offset().top + $(settings.container).height();
        }
        return fold <= $(element).offset().top - settings.threshold;
    };
    $.rightoffold = function(element, settings) {
        var fold;
        if (settings.container === undefined || settings.container === window) {
            fold = $window.width() + $window.scrollLeft();
        } else {
            fold = $(settings.container).offset().left + $(settings.container).width();
        }
        return fold <= $(element).offset().left - settings.threshold;
    };
    $.abovethetop = function(element, settings) {
        var fold;
        if (settings.container === undefined || settings.container === window) {
            fold = $window.scrollTop();
        } else {
            fold = $(settings.container).offset().top;
        }
        return fold >= $(element).offset().top + settings.threshold  + $(element).height();
    };
    $.leftofbegin = function(element, settings) {
        var fold;
        if (settings.container === undefined || settings.container === window) {
            fold = $window.scrollLeft();
        } else {
            fold = $(settings.container).offset().left;
        }
        return fold >= $(element).offset().left + settings.threshold + $(element).width();
    };
    $.inviewport = function(element, settings) {
         return !$.rightoffold(element, settings) && !$.leftofbegin(element, settings) &&
                !$.belowthefold(element, settings) && !$.abovethetop(element, settings);
    };
    $.extend($.expr[":"], {
        "below-the-fold" : function(a) { return $.belowthefold(a, {threshold : 0}); },
        "above-the-top"  : function(a) { return !$.belowthefold(a, {threshold : 0}); },
        "right-of-screen": function(a) { return $.rightoffold(a, {threshold : 0}); },
        "left-of-screen" : function(a) { return !$.rightoffold(a, {threshold : 0}); },
        "in-viewport"    : function(a) { return $.inviewport(a, {threshold : 0}); },
        "above-the-fold" : function(a) { return !$.belowthefold(a, {threshold : 0}); },
        "right-of-fold"  : function(a) { return $.rightoffold(a, {threshold : 0}); },
        "left-of-fold"   : function(a) { return !$.rightoffold(a, {threshold : 0}); }
    });
})(jQuery, window, document);
<!-- js引入文件结束 -->

js图片预加载记录demo示例（整理）

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