When loading Vue and Element-UI cascading drop-down box data asynchronously, performance problems should be encountered due to large amounts of data: preload all or part of the data, build a tree structure, and recursive rendering; optimize the loading strategy, only asynchronously load the secondary node after selecting the first-level node, reducing network requests; handle errors and add caches to avoid duplicate requests; consider paging loading or virtual scrolling technology to process massive data.

Vue and Element-UI cascaded drop-down boxes load data asynchronously: Don't be confused by appearances!

You must have seen those cascading selectors that look cool, which can load layers of nested data in a flash, right? But behind this, there are many pitfalls of asynchronous loading! This article will take you to avoid the crazy traps and write fast and stable code. After reading it, you can easily control the asynchronous cascade selector and even write code that is more efficient than many ready-made components.

Let’s talk about the basics first, you need to understand what Vue and Element-UI are. Vue, you know, is a popular JavaScript framework; Element-UI, a Vue-based UI component library, provides many ready-made components, including cascading selectors. Asynchronous loading, to put it bluntly, the data is not prepared from the beginning, but loading on demand to avoid loading a large amount of data at one time causing the page to stutter.

Element-UI's cascading selector itself supports asynchronous loading, but its default implementation method may not be ideal in case of large data volumes. Why? Because it defaults to request data every time you select a node. Imagine that if your data structure is deep, it will trigger many network requests, and the user experience will definitely be poor.

So, we need smarter strategies. A good idea is to preload all the data, or at least load to a certain depth. This requires reasonable organization and preprocessing of the data. For example, you can build a tree structure data and then render it recursively in the component.

Let’s look at a piece of code. I am using a more optimized solution. It obtains the data of all first-level nodes when loading for the first time, and then loads the data of the second-level node asynchronously after the user selects the first-level node. In this way, the number of network requests can be reduced and performance can be improved.

 <code class="javascript"><template> <el-cascader v-model="selectedOptions" :options="options" :props="props" placeholder="請選擇"></el-cascader> </template> <script> import { ref, reactive } from &#39;vue&#39;; export default { setup() { const selectedOptions = ref([]); const options = ref([]); const props = reactive({ label: &#39;label&#39;, value: &#39;value&#39;, children: &#39;children&#39;, }); const loadFirstLevel = async () => { const res = await fetch(&#39;/api/first-level&#39;); // 這里替換成你的API const data = await res.json(); options.value = data; }; const loadChildren = async (value) => { const res = await fetch(`/api/children?parentId=${value}`); // 這里替換成你的API const data = await res.json(); const node = findNode(options.value, value); node.children = data; }; const findNode = (arr, value) => { for (let i = 0; i < arr.length; i ) { if (arr[i].value === value) { return arr[i]; } if (arr[i].children && arr[i].children.length > 0) { const node = findNode(arr[i].children, value); if (node) return node; } } return null; }; const handleChange = (value) => { if (value.length > 1) { const parentId = value[value.length - 2]; loadChildren(parentId); } }; loadFirstLevel(); return { selectedOptions, options, props, handleChange }; }, }; </script></code>

The key to this code is the two asynchronous functions, loadFirstLevel and loadChildren , which are respectively responsible for loading the data of first-level nodes and children. The findNode function is used to find nodes in the loaded data. The handleChange function triggers asynchronous loading when the user selects a node. Remember, this is just an example, you need to adjust it according to your actual API interface.

Don't forget to handle the error! Network requests may fail, you need to add an error handling mechanism, such as displaying error prompt information. Also, consider data caching to avoid repeated requests to the same data. Also, if the data volume is extremely large, you may need to consider paging loading, or using virtual scrolling techniques.

In short, asynchronous loading of cascading selectors seems simple, but actually requires careful consideration of performance and user experience. Don't be confused by those simple examples. You must deeply understand the principles in order to write efficient and stable code. Remember, the elegance of the code is reflected in the processing of details. Think more and practice more and you can become a master of cascading selectors!

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