render function in Vue3: custom rendering function

Vue is a popular JavaScript framework that provides many convenient functions and APIs to help developers build interactive front-end applications. With the release of Vue 3, the render function has become an important update. This article will introduce the concept and purpose of the render function in Vue3 and how to use it to customize the rendering function.

What is the render function

In Vue, template is the most commonly used rendering method, but in Vue3, you can use another method: the render function. The Render function is an ordinary JavaScript function that converts data into HTML elements.

Some people may think that template is easier to understand and use than render function. However, when the application becomes more complex, using the Render function can improve performance and maintainability. In addition, the Render function can control rendering output in a more direct way.

How to use the render function

In Vue3, you can use the render function as a property of the component. When a component is instantiated, the render function is called to render the component's state into HTML. The following is the basic API of the render function:

render(createElement) {
    return createElement('div', 'Hello Vue 3!')
}

The code above uses the createElement function to create a div element and then returns it. Eventually, in the view's HTML, a div element will be rendered containing the text "Hello Vue 3!"

Of course, the above code is very simple. Render functions often require more complex logic, such as generating repeated elements through a loop. The following is a simple example containing conditional statements and loop logic:

render(createElement) {
    if (this.displayText) {
        return createElement('div', {
            attrs: {
                class: 'container'
            }
        }, [
            createElement('h1', 'My Todo List'),
            createElement('ul', this.todos.map((todo) => {
                return createElement('li', todo)
            })),
            createElement('button', {
                on: {
                    click: this.printHello
                }
            }, 'Click me')
        ])
    } else {
        return createElement('div', 'Nothing to display')
    }
}

The above code checks if the displayText property is true, if so, the Todo list is rendered, otherwise, only the "Nothing to display" text will be displayed. In the rendering of the list, we loop to generate a li element for each Todo.

Benefits of the render function in Vue3

In Vue3, the render function greatly improves the maintainability, testability and performance of the application. The following are several advantages provided by the render function:

More direct control

The Render function provides more direct control over rendering output than template because it is a normal JavaScript function. This means developers can leverage regular JavaScript control structures, such as loops and conditional statements, to customize more of the rendering output.

Better Performance

Templates are compiled dynamically at runtime, which increases application load time. In contrast, Render functions are created at compile time, which means they can be parsed and rendered directly in the browser without additional compilation overhead. This further improves application performance.

Easier to test

Rendering functions are implemented in pure JavaScript, which makes it easier to write unit and integration tests. Test the rendering function, which can be tested against different input values ​​to verify whether the output meets expectations.

More flexible parameters

The rendering function builds DOM elements through the createElement function. This means that rendering functions can accept more flexible parameters, such as computed properties and methods, as well as props and slots. This allows developers to easily compose and reuse components.

Summary

The render function in Vue3 is an important part of Vue enhancement. It provides developers with the advantages of more direct control, better performance, and easier testing. Use the Render function to freely control the output of the UI, while improving the maintainability and testability of the application.

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