JavaScript scroll bar events are not real-time

In web development, we often need to use JavaScript to implement dynamic scrolling of elements on the page, and we need to control scrolling events to achieve the best user experience and interactive effects. However, in some cases, we may encounter such a problem: the scroll bar events are not real-time or the response is not timely. This kind of problem often causes the scrolling effect of the page to be unsmooth and affects the user experience. This article will discuss both technical principles and solutions.

1. Technical Principle

To understand why scroll bar events are not real-time, you need to have a certain understanding of the event binding mechanism in JavaScript. The event mechanism in JavaScript is implemented based on the browser event model. Event binding associates a function with a specific event. When this event fires, the function associated with it will be called. For scroll bar events, the scroll event of the window object is usually used. This event is triggered when the page is scrolled. If the scroll bar event does not respond in time, it means that the browser failed to trigger the scroll event in time. This usually occurs in the following two situations:

1. The function execution time is too long

When the function we bind in the scroll event takes too long to execute, the browser may not be able to respond to the scroll bar event in time. For example, when we are scrolling the page, if there are complex calculations or DOM operations at the same time, it will cause the scroll bar event to not respond in time.

2. Too many page elements

When there are a large number of elements on the page, the scroll bar event will also not respond in time. Because the browser needs to render and redraw each element when scrolling, if there are too many elements, the response speed will be slower.

2. Solution

In response to the above problems, we can adopt the following two solutions to solve the problem of non-real-time scroll bar events.

1. Function execution optimization

Optimizing the function execution in the scroll event is an important method to solve the problem of slow response to scroll bar events. We can optimize in the following ways:

(1) Cache DOM elements

When the function is executed, if we need to operate DOM elements, we can first cache the elements that need to be operated, so that It can reduce the number of DOM queries and improve function execution speed.

(2) Function throttling

Function throttling refers to a method of controlling the frequency of function calls by delaying function execution. We can use the throttling function to limit the triggering frequency of the scroll event and reduce the number of executions of the function. For example, the following is a simple function throttling implementation code:

function throttle(fn, delay) {
    let timer = null;
    return function() {
        let context = this, args = arguments;
        clearTimeout(timer);
        timer = setTimeout(function() {
            fn.apply(context, args);
        }, delay);
    };
}

In the above function, we set a timer to delay the execution of the function, thereby controlling the frequency of function calls.

(3) Function anti-shake

Function anti-shake means to delay the execution of the function for a period of time after the event is triggered. If the event is triggered again during this period, the timing will be restarted. We can limit the response time of the scroll event through function anti-shake. For example, the following is a simple function anti-shake implementation code:

function debounce(fn, delay) {
    let timer = null;
    return function() {
        let context = this, args = arguments;
        clearTimeout(timer);
        timer = setTimeout(function() {
            fn.apply(context, args);
        }, delay);
    };
}

In the above function, we also set a timer to delay the execution of the function, but if the same event is triggered during the delay period, then Retime, so that the response time of the scroll event can be limited.

2. Reduce page elements

When there are too many page elements, we can also solve the problem of slow response to scroll bar events by reducing page elements. The specific method is as follows:

(1) DOM element cleaning

When the page is scrolling, we can clear some unnecessary DOM elements by listening to the scroll event, thereby reducing the amount of time the browser needs to render. Number of elements.

(2) Paging loading

In some pages that require a large amount of data to be displayed, we can use page loading to load data into the page in batches to avoid loading a large amount of data at once. Resulting in performance degradation.

Summary

In Web development, the response speed of scroll bar events is crucial to the interactive experience of the page. By optimizing function execution in scroll events and reducing page elements, we can effectively solve the problem of non-real-time scroll bar events and improve page performance and user experience.

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