Some Vue code optimization tips

Vue is a popular JavaScript framework that can quickly build data-driven web applications. However, as Vue projects become more and more complex, optimizing the code becomes particularly important. If you don't optimize your code, your application's performance can be slow and your code more difficult to maintain. This article will introduce some Vue code optimization techniques.

1. Avoid using complex calculations in templates

Vue provides the function of calculating properties. Computed properties convert the value of a reactive object into a computed property that can be used for rendering. This makes using computed properties more efficient than using complex calculations directly in the template. If the data on which the calculated attribute depends does not change, the computed value will only be calculated once when used multiple times in the template.

Suppose there is a piece of code in the template:

<div>{{ items.filter(item => item.price > 10).map(item => item.name) }}</div>

This code will calculate the item array every time it is re-rendered, so if the item array is large, this will cause performance problems. Instead, you can use calculated properties to calculate the results. The calculated properties will be recalculated when the dependencies change:

computed: {
  filteredItems() {
    return this.items.filter(item => item.price > 10)
  },
  itemNames() {
    return this.filteredItems.map(item => item.name)
  }
}

The corresponding template code will become:

<div>{{ itemNames }}</div>

This method can significantly improve Application performance.

2. Avoid using nested v-if and v-for in templates

In templates, v-if and v-for are two very powerful directives . However, when these two instructions are nested together, they become very slow. For example:

<div v-for="user in users" v-if="user.isActive">{{ user.name }}</div>

This code uses v-for to traverse the users array, and then uses v-if to filter out the elements whose isActive is true. This process is very inefficient. Vue calculates the entire list multiple times and recreates the DOM elements each time.

In order to improve performance, you can change v-if and v-for to computed attributes:

computed: {
  activeUsers() {
    return this.users.filter(user => user.isActive)
  }
}

Then use v-for in the template to traverse activeUsers:

<div v-for="user in activeUsers">{{ user.name }}</div>

3. Reduce the number of Watchers

watcher provides a responsive update mechanism for Vue data. When a property changes, the watcher will automatically update the related views. However, if there are too many watchers, it can cause performance problems. Generally, the number of watchers is proportional to the number of properties of the Vue instance.

In order to reduce the number of watchers, you can use the computed attribute instead of watcher. Computed properties are only recomputed when dependencies change, whereas watchers are always called on every property change. If you don't need to update the view every time a property changes, computed properties are a better choice.

4. Optimize list rendering

In Vue, list rendering is a very common task. To optimize list rendering, you can use the key attribute. The key attribute is an ID that distinguishes each item in the list. It allows Vue to detect changes in DOM elements faster and restore state faster when rendering the same list item repeatedly.

However, please be careful not to use dynamic keys in large lists. Using dynamic keys will cause Vue to re-render the entire list, which will be very performance-intensive. Instead, use key, but make sure it is static and unique across the list.

5. Using asynchronous components

Vue provides asynchronous component functionality, which allows us to delay the loading of components, thereby increasing the initialization speed of the application. If we have a large component or page, we can optimize it in this way to make the first page of the page load faster. Using Vue's asynchronous component functionality requires the use of similar packaging tools such as Webpack.

6. Performance testing using Vue Devtools

Vue Devtools is a browser extension for debugging Vue applications. It not only provides the hierarchy and state of Vue components, but also allows you to check the performance of your application. With Devtools' performance analysis, you can rigorously examine performance issues and track actual performance to identify the slowest code paths and what may be causing them. This is a great tool for optimizing the performance of Vue applications.

Summary:

The above are some tips for optimizing the performance of Vue applications. The performance of your Vue application can be significantly improved by avoiding complex calculations in templates, optimizing list rendering, asynchronous components that affect first screen time, etc. Finally, using Vue Devtools is a great way to detect and resolve application performance issues.

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