How to implement lazy-loading image components in Vue?

Vue is a popular front-end framework that provides many powerful features and components, including image components. During web development, loading a large number of images may cause the website to slow down. In order to reduce this pressure, we can implement the image component in a simulated lazy loading manner so that the website can load and be presented to users faster.

In this article, we will learn how to use Vue to implement a lazy-loaded image component, which includes the following steps:

1. Build a basic image component
2. Add the function of imitating delayed loading
3. Testing and optimization

Next, we will explain it step by step.

1. Build a basic picture component

First, we need to create a basic picture component so that we can add more functions in subsequent steps. You can use the Vue CLI command line tool to create a basic Vue project and add an image component to it. In this component, we can use Vue's built-in directive v-bind to bind the src attribute of the image and define a default alt text.

Code example:

<template>
  <img v-bind:src="src" alt="Image">
</template>

<script>
export default {
  name: "ImageComponent",
  props: {
    src: {
      type: String,
      required: true,
    },
  },
};
</script>

Next, we can use this component to load our image resources.

2. Add the function of imitation lazy loading

Next, we will use the features of Vue to add the function of imitation lazy loading. When the website is initialized, we only need to load the image content of the visible part of the page, and other content will be loaded when the user scrolls the page. To do this, we need to use Vue's built-in instruction v-once to load the image to ensure that each component will only be rendered once. We will then use Vue's lifecycle function mounted to check if the component is within the visible area and act accordingly.

In this example, we will use the Intersection Observer API to detect whether the element is within the visible area. If the element is within the visible area, we load the image. If the element is not within the visible area, nothing is done. Below is a simple implementation.

Code example:

<template>
  <div ref="imageWrapper">
    <img v-bind:src="src" alt="Image" v-once>
  </div>
</template>

<script>
export default {
  name: "ImageComponent",
  props: {
    src: {
      type: String,
      required: true,
    },
  },
  mounted() {
    const observer = new IntersectionObserver(
      ([entry]) => {
        if (entry.isIntersecting) {
          this.$refs.imageWrapper.classList.add('loaded');
          observer.disconnect();
        }
      },
      {
        rootMargin: "50px 0px",
      }
    );
    observer.observe(this.$refs.imageWrapper);
  },
};
</script>

<style>
  .loaded img {
    opacity: 1;
    transition: opacity 0.5s ease-in;
  }

  img {
    opacity: 0;
  }
</style>

In this implementation, we place the image component in a div element containing the ref attribute, and add a class named loaded to this element. In the mounted lifehook function, we use the IntersectionObserver API to detect whether the div element is within the visible area. If the element is within the visible area, we will add a class named loaded to the div element, which contains an opacity attribute that increases the transparency of the image from 0 to 1. By adding this class, we can use CSS transition effects to implement the gradient loading process of images.

3. Testing and Optimization

Up to this point, we have successfully implemented a delayed-loading image component. Now, we can use this component in our Vue project to load our image resources. However, in order to achieve better site performance, we still need further testing and optimization.

To test the performance of components, we can use developer tools to simulate a slow Internet connection. By testing the page loading speed on a slower network speed, we can better understand the performance and optimization direction of the component.

In addition, we can also optimize the rootMargin (root margin) and threshold (threshold) of the Intersection Observer API to make the component better adaptable under different devices and resolutions. We can adjust root margins and thresholds to determine when a crossover is recorded, and record the optimization information in a monitoring tool for further analysis and improvement.

Summary

In this article, we learned how to use Vue to implement a lazy-loaded image component. We first created a basic image component and added a simulated lazy loading function using Vue's features. Finally, we also discuss how to test and optimize this component.

Through this implementation, we can make the website load image resources faster, and load other parts of the image when the user slides the page, thus improving the user experience.

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