jquery select does not refresh

JQuery is a very powerful JavaScript library that provides a series of tools and methods that can make front-end development easier and more efficient. Among them, JQuery select is a commonly used component, used to implement interactive controls such as drop-down boxes and check boxes. However, when using JQuery select, sometimes you will encounter a situation where it does not refresh. This article explains why this happens and how to fix it.

First of all, we need to understand the principle of JQuery select. JQuery select is implemented based on the HTML select element. When the page loads, JQuery will scan the select element on the page and encapsulate it into a JQuery object. Then, JQuery will add event listeners to these objects. When the user selects an option, JQuery will trigger the corresponding event and update the value of the select element.

However, sometimes we will find that although the user selects different options, the value of the select element does not change. This situation is usually caused by two reasons: one is the use of a caching mechanism, and the other is the modification of the HTML structure of the select element.

The first case, that is, the caching mechanism is used, because JQuery select is implemented based on the HTML select element, and the value of the HTML select element is stored in memory. Therefore, if we use the caching mechanism, when modifying the options of the select element, its value will not change immediately, but will wait for the next page refresh to update.

In order to solve this problem, we can use the val() method provided by JQuery to get the currently selected value. This method will get the value of the current select element directly from memory instead of from the cache. Therefore, when we use the select element, we can use the val() method to obtain the currently selected value instead of directly accessing the value attribute of the select element.

The second case, that is, the HTML structure of the select element is modified because JQuery select encapsulates the HTML select element into a JQuery object and then adds an event listener for it. If we directly modify the HTML structure of the select element, these event listeners may become invalid, causing the select element to not update the value correctly.

In order to solve this problem, we can use the on() method provided by JQuery to listen to the event of the select element. This method will add a listener to the parent element of the select element to ensure that the listener can still work properly when the HTML structure of the select element is modified.

Finally, there is another situation that may cause JQuery select not to refresh, that is, calling JQuery's select method multiple times. The JQuery select method itself adds event listeners to each select element and returns a new JQuery object after being called. If we call the select method multiple times to add event listeners to the same select element, these listeners may interfere with each other, causing the select element to not update the value correctly.

In order to avoid this problem, we should try to avoid calling the select method multiple times. If you need to dynamically modify the options of the select element, you can use the append(), remove(), empty() and other methods provided by JQuery to achieve this.

In short, the problem of JQuery select not refreshing is usually caused by using the caching mechanism, modifying the HTML structure, or calling the select method multiple times. By using the val(), on() and other methods provided by JQuery, we can avoid these problems and achieve correct update of the select element. At the same time, we also need to pay attention not to frequently use the caching mechanism and call methods multiple times when using JQuery select, so as to avoid possible problems.

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