Title: Master the top attribute in jQuery setting css attributes

As a front-end developer, it is very important to master the skills of jQuery operating DOM elements. Among them, setting css properties is one of the most basic and commonly used operations. This article will focus on how to use jQuery to set the top attribute in css attributes.

1. What is the top attribute

In CSS, the top attribute is a method of setting the position of an element relative to the top of its parent element. Typically, the attribute value is in pixels (px), and the value range is negative, 0, and positive. For example, when the top value is 10px, it means that the element is offset downward by 10 pixel units relative to the top border of its parent element.

2. How jQuery sets the css top attribute

jQuery provides some methods that can be used to set the css attribute of an element. Among them, there are two ways to set the top attribute: .css() method and .animate() method.

1. Use the .css() method

.css() method to directly set the CSS properties of the element.

The syntax format is as follows:

$(selector).css(property,value)

Among them, property represents the CSS attribute to be set, and value represents the attribute value to be set. .

For example, the following code can set the top attribute of the element id myDiv:

$("#myDiv").css("top", "10px");

2. Use the .animate() method

The .animate() method is used to set the animation effect of the element. Setting the top attribute of an element can also be achieved through the animate method. Unlike the css method, the animate method can set the animation time and provide some animation effects. For example, we want to move the element id myDiv downward by 50 pixels and the animation duration is 2 seconds (note: the top attribute in CSS sets a relative position, and the relative position here is the position 50px downward from the original position):

$("#myDiv").animate({ top: " =50px"}, 2000);

The top here: " =50px" means changing the element id to the original position of myDiv Add 50 pixels to the top attribute value.

3. Classic Case

Below, we use a classic case to demonstrate how to use jQuery to set the top attribute of an element. This case is to implement a fixed floating box on the page. When the page scrolls down to a certain distance, the floating box scrolls with the page and remains at the top.

HTML code:

... 正文内容 ...

CSS code:

header {

position: fixed;
top: 0;
background-color: #fff;
width: 100%;
height: 60px;
z-index: 999;
}

content {

padding-top: 60px;
}

JavaScript code:

$(window).scroll(function() {
// Get the scrolling distance of the current page
var scrollTop = $(window).scrollTop();
// Get the height of the floating box
var headerHeight = $("#header").height() ;
// Set the top attribute of the floating box
if (scrollTop > headerHeight) {

$("#header").css("top", scrollTop - headerHeight);

} else {

$("#header").css("top", "0px");

}
});

The implementation principle of the above code is: when the page scrolls down, obtain the scrollTop distance of the current page and the height headerHeight of the floating box through js, and then determine whether the page has scrolled to a certain distance. If so, the floating box will be Set the top attribute value to scrollTop - headerHeight to make it scroll with the page; if not, set the top attribute value of the floating box to 0px to fix it at the top of the page.

4. Summary

Through the introduction of this article, we understand what the top attribute is and how to use jQuery to set the top attribute of an element. At the same time, a practical case is also given to help readers better understand how to use jQuery to operate page elements. After learning, readers can flexibly use css and jQuery to achieve more beautiful page effects.

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