Implementation steps: 1. Use the jquery selector to obtain the specified element object, the syntax "$(selector)"; 2. Use the attr() method to obtain the attribute value of the specified attribute of the jquery object, the syntax "element object" .attr("attribute name")"; 3. Use the "==" operator to determine whether the obtained attribute value is equal to undefined. The syntax is "attribute value =='undefined'". If it is equal, an attribute will not be included, otherwise it will be included. .
The operating environment of this tutorial: windows7 system, jquery3.6.1 version, Dell G3 computer.
In jquery, to determine whether an element has a certain attribute, the attr() method is mainly used. Through this method, the obtained attribute value can be judged to determine whether the element has a certain attribute.
Implementation steps:
Step 1: Use jquery selector to obtain the specified element object
$(selector)
Will return a jquery object containing the specified element
Step 2: Use the attr() method to obtain the value of the specified attribute of the jquery object
元素对象.attr("属性名")
Will return the attribute value of the specified attribute
Step 3: Use the "==" operator to determine whether the obtained attribute value is equal to undefined
属性值=='undefined'
If equal, then do not include a certain attribute
If not equal, then include a certain attribute
Implementation example:
Determine whether the input element has a name attribute
<!DOCTYPE html> <html> <head> <meta charset="utf-8" /> <script src="js/jquery-3.6.0.min.js"></script> <script> $(document).ready(function() { $("button").click(function() { var value=$("input").attr("name"); if(value=='undefined'){ console.log("不包含name属性") } else{ console.log("包含name属性") } }); }); </script> </head> <body> <form action="form_action.asp" method="get"> <p>name:<input type="text" name="fullname" /></p> <p>email:<input type="text" name="email" /></p> </form> <button>判断input元素是否有name属性</button> </body> </html>
[Recommended Learning: jQuery video tutorial, web front-end video】
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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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