我正在使用的插件中有一行我试图理解：
$self.hide().attr("src", $self.data(settings.data_attribute))[settings.effect](settings.effect_speed);
self 是一个 jquery 对象，在这段代码中是一个 img dom 元素，它隐藏它，然后将此 img 对象的 src 属性设置为 html5 数据属性。但现在它访问由.attr（返回的jquery对象中的一个属性，在这个中是“fadeIn”。但我不明白，jquery对象是否有内置的效果属性函数内置到jquery对象中？我很困惑这如何转化为调用 .fadeIn(900)。我在 jquery 网站上的任何地方都找不到此文档。如果有人能对此有所了解，谢谢。
抱歉，这是完整的代码，它来自 mika tuupola 的延迟加载 jquery 插件：
(function($, window, document, undefined) {
var $window = $jq191(window);
$jq191.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 : true,
appear : null,
load : null
};
function update() {
var counter = 0;
elements.each(function() {
var $this = $jq191(this);
if (settings.skip_invisible && !$this.is(":visible")) {
return;
}
if ($jq191.abovethetop(this, settings) ||
$jq191.leftofbegin(this, settings)) {
/* Nothing. */
} else if (!$jq191.belowthefold(this, settings) &&
!$jq191.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) {
/* Maintain BC for a couple of versions. */
if (undefined !== options.failurelimit) {
options.failure_limit = options.failurelimit;
delete options.failurelimit;
}
if (undefined !== options.effectspeed) {
options.effect_speed = options.effectspeed;
delete options.effectspeed;
}
$jq191.extend(settings, options);
}
/* Cache container as jQuery as object. */
$container = (settings.container === undefined ||
settings.container === window) ? $window : $jq191(settings.container);
/* Fire one scroll event per scroll. Not one scroll event per image. */
if (0 === settings.event.indexOf("scroll")) {
$container.bind(settings.event, function(event) {
return update();
});
}
this.each(function() {
var self = this;
var $self = $jq191(self);
self.loaded = false;
/* When appear is triggered load original image. */
$self.one("appear", function() {
if (!this.loaded) {
if (settings.appear) {
var elements_left = elements.length;
settings.appear.call(self, elements_left, settings);
}
$jq191("<img />")
.bind("load", function() {
$self
.hide()
.attr("src", $self.data(settings.data_attribute))
[settings.effect](settings.effect_speed);
self.loaded = true;
/* Remove image from array so it is not looped next time. */
var temp = $jq191.grep(elements, function(element) {
return !element.loaded;
});
elements = $jq191(temp);
if (settings.load) {
var elements_left = elements.length;
settings.load.call(self, elements_left, settings);
}
})
.attr("src", $self.data(settings.data_attribute));
}
});
/* When wanted event is triggered load original image */
/* by triggering appear. */
if (0 !== settings.event.indexOf("scroll")) {
$self.bind(settings.event, function(event) {
if (!self.loaded) {
$self.trigger("appear");
}
});
}
});
/* Check if something appears when window is resized. */
$window.bind("resize", function(event) {
update();
});
/* With IOS5 force loading images when navigating with back button. */
/* Non optimal workaround. */
if ((/iphone|ipod|ipad.*os 5/gi).test(navigator.appVersion)) {
$window.bind("pageshow", function(event) {
if (event.originalEvent.persisted) {
elements.each(function() {
$jq191(this).trigger("appear");
});
}
});
}
/* Force initial check if images should appear. */
$jq191(window).load(function() {
update();
});
return this;
};
/* Convenience methods in jQuery namespace. */
/* Use as $jq191.belowthefold(element, {threshold : 100, container : window}) */
$jq191.belowthefold = function(element, settings) {
var fold;
if (settings.container === undefined || settings.container === window) {
fold = $window.height() + $window.scrollTop();
} else {
fold = $jq191(settings.container).offset().top + $jq191(settings.container).height();
}
return fold <= $jq191(element).offset().top - settings.threshold;
};
$jq191.rightoffold = function(element, settings) {
var fold;
if (settings.container === undefined || settings.container === window) {
fold = $window.width() + $window.scrollLeft();
} else {
fold = $jq191(settings.container).offset().left + $jq191(settings.container).width();
}
return fold <= $jq191(element).offset().left - settings.threshold;
};
$jq191.abovethetop = function(element, settings) {
var fold;
if (settings.container === undefined || settings.container === window) {
fold = $window.scrollTop();
} else {
fold = $jq191(settings.container).offset().top;
}
return fold >= $jq191(element).offset().top + settings.threshold + $jq191(element).height();
};
$jq191.leftofbegin = function(element, settings) {
var fold;
if (settings.container === undefined || settings.container === window) {
fold = $window.scrollLeft();
} else {
fold = $jq191(settings.container).offset().left;
}
return fold >= $jq191(element).offset().left + settings.threshold + $jq191(element).width();
};
$jq191.inviewport = function(element, settings) {
return !$jq191.rightoffold(element, settings) && !$jq191.leftofbegin(element, settings) &&
!$jq191.belowthefold(element, settings) && !$jq191.abovethetop(element, settings);
};
/* Custom selectors for your convenience. */
/* Use as $jq191("img:below-the-fold").something() or */
/* $jq191("img").filter(":below-the-fold").something() which is faster */
$jq191.extend($jq191.expr[':'], {
"below-the-fold" : function(a) { return $jq191.belowthefold(a, {threshold : 0}); },
"above-the-top" : function(a) { return !$jq191.belowthefold(a, {threshold : 0}); },
"right-of-screen": function(a) { return $jq191.rightoffold(a, {threshold : 0}); },
"left-of-screen" : function(a) { return !$jq191.rightoffold(a, {threshold : 0}); },
"in-viewport" : function(a) { return $jq191.inviewport(a, {threshold : 0}); },
/* Maintain BC for couple of versions. */
"above-the-fold" : function(a) { return !$jq191.belowthefold(a, {threshold : 0}); },
"right-of-fold" : function(a) { return $jq191.rightoffold(a, {threshold : 0}); },
"left-of-fold" : function(a) { return !$jq191.rightoffold(a, {threshold : 0}); }
});
})($jq191, 窗口, 文档);