There are many introductions about jQuery's this and $(this) on the Internet. Most of them just clarify the directions of this and $(this). In fact, they have applications and cannot be generalized. When jQuery calls member functions, this points to the dom object.
It is understandable that$(this) points to the jQuery object, but this points to the dom object. This is because jQuery has done special processing.
When creating a jQuery object of dom, jQuery not only creates a jQuery object for dom, but also stores dom in the array of the created object.
elem = document.getElementById(match[2]);
if (elem && elem.parentNode) {
This.length = 1;
this[0] = elem;
}
this.context = document;
this.selector = selector;
return this;
The statement this[0] = elem implements an object array. So JavaScript is a very interesting language. When using this to access, you can access the member functions of the object it points to, and in fact this is an array of objects. It stores dom objects.
Let’s take a look at $("p").each() -- loop
each: function( callback, args ) {
return jQuery.each( this, callback, args );
}
After reading the call of each function, you should understand that jQuery.each( this, callback, args ); calls an array of objects, and the array of objects stores dom objects, so this in the callback function is naturally dom Target
Look again at $("p").hide() --Member function
hide: function() {
return showHide( this );
},
function showHide( elements, show ) {var elem, display,
values = [],
index = 0,
length = elements.length;
for ( ; index elem = elements[ index ];
if ( !elem.style ) {
continue;
}
values[ index ] = jQuery._data( elem, "olddisplay" );
if ( show ) {
// Reset the inline display of this element to learn if it is
// being hidden by cascaded rules or not
if ( !values[ index ] && elem.style.display === "none" ) {
elem.style.display = "";
}
// Set elements which have been overridden with display: none
// in a stylesheet to whatever the default browser style is
// for such an element
if ( elem.style.display === "" && isHidden( elem ) ) {
values[ index ] = jQuery._data( elem, "olddisplay", css_defaultDisplay(elem.nodeName) );
}
} else {
display = curCSS( elem, "display" );
if ( !values[ index ] && display !== "none" ) {
jQuery._data( elem, "olddisplay", display );
}
}
}
// Set the display of most of the elements in a second loop
// to avoid the constant reflow
for ( index = 0; index elem = elements[ index ];
if ( !elem.style ) {
continue;
}
if ( !show || elem.style.display === "none" || elem.style.display === "" ) {
elem.style.display = show ? values[ index ] || "" : "none";
}
}
return elements;
}
从上面的代码可以看出hide行数其实调用的是showHide,而传入的第一个参数this,并不是dom对象,而是jQuery对象数组,因此showHide函数通过循环此对象数组获取每一个dom对象。
最后看看$("p").bind() -- 事件
bind: function( types, data, fn ) {
return this.on( types, null, data, fn );
},
on: function( types, selector, data, fn, /*INTERNAL*/ one ) {
// This part of the code is omitted
return this.each( function() { jQuery.event.add( this, types, fn, data, selector );
});
},

实现方法:1、用“$("img").delay(毫秒数).fadeOut()”语句,delay()设置延迟秒数;2、用“setTimeout(function(){ $("img").hide(); },毫秒值);”语句,通过定时器来延迟。

修改方法:1、用css()设置新样式,语法“$(元素).css("min-height","新值")”;2、用attr(),通过设置style属性来添加新样式,语法“$(元素).attr("style","min-height:新值")”。

区别:1、axios是一个异步请求框架,用于封装底层的XMLHttpRequest,而jquery是一个JavaScript库,只是顺便封装了dom操作;2、axios是基于承诺对象的,可以用承诺对象中的方法,而jquery不基于承诺对象。

增加元素的方法:1、用append(),语法“$("body").append(新元素)”,可向body内部的末尾处增加元素;2、用prepend(),语法“$("body").prepend(新元素)”,可向body内部的开始处增加元素。

在jquery中,apply()方法用于改变this指向,使用另一个对象替换当前对象,是应用某一对象的一个方法,语法为“apply(thisobj,[argarray])”;参数argarray表示的是以数组的形式进行传递。

删除方法:1、用empty(),语法“$("div").empty();”,可删除所有子节点和内容;2、用children()和remove(),语法“$("div").children().remove();”,只删除子元素,不删除内容。

去掉方法:1、用“$(selector).removeAttr("readonly")”语句删除readonly属性;2、用“$(selector).attr("readonly",false)”将readonly属性的值设置为false。

on()方法有4个参数:1、第一个参数不可省略,规定要从被选元素添加的一个或多个事件或命名空间;2、第二个参数可省略,规定元素的事件处理程序;3、第三个参数可省略,规定传递到函数的额外数据;4、第四个参数可省略,规定当事件发生时运行的函数。


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