v-once, v-html

Vue.js provides two useful directives, v-once, and v-html, to enhance template functionality. In this topic, we'll delve into the syntax, usage, examples, and best practices for both v-once and v-html. Through practical examples, we'll explore scenarios where v-once proves beneficial for static content, and v-html becomes a valuable tool for rendering HTML dynamically.

What is v-once and v-html

The Role of v-once: The v-once directive is a handy tool for optimizing rendering performance. When applied to an element, it ensures that the element and its children are only evaluated once and do not update on subsequent re-renders. This is particularly useful when dealing with static content that doesn't change throughout the component's lifecycle.

The Role of v-html: On the other hand, the v-html directive is employed when you need to render HTML content dynamically. It allows you to bind a variable containing HTML code to an element, interpreting it as actual HTML rather than plain text. While powerful, it comes with certain considerations, especially regarding potential security risks, which we will explore later.

Syntax

1. v-once:

<template>
  <div v-once>
  <!-- Static content that won't change --> 
  </div>
</template>

<script setup>

// Component logic

</script>

2. v-html:

<template>
  <div v-html="renderedHtml"></div>
</template>

<script setup>

// Component logic
const renderedHtml = ref('<p>This is HTML content.</p>');

</script>

Example and usage

In Vue.js, v-once and v-html are two directives that can be used to enhance the functionality of your templates. Let's explore each one in detail, along with examples:

1. v-once:

The v-once directive is used to render content only once as we discussed above. This means that the expression or content associated with v-once will be evaluated and rendered only once, and subsequent changes to the data will not affect it. Let's take this into account in the below example:

<template>
  <h1 v-once>{{ title }}</h1>
  <p>This paragraph will be re-evaluated on data changes: {{ dynamicContent }}</p>
</template>

<script setup>
import { ref } from 'vue';

// Static data that won't change
const title = 'Static Title';

// Dynamic content that may change
const dynamicContent = ref('Initial Dynamic Content');

// Simulate some logic that changes dynamicContent
setTimeout(() => {
  dynamicContent.value = 'Updated Dynamic Content';
}, 2000);
</script>

In the above example, when the component is initially rendered, the h1 element displays the static title (Static Title) and the p element displays the initial dynamic content (Initial Dynamic Content). After 2 seconds, the dynamic content is updated, but the h1 element with v-once remains the same. This helps in scenarios where you have static content that doesn't need to be re-evaluated frequently for performance reasons.

2. v-html:

The v-html directive is used to render HTML content dynamically. It allows you to bind a property containing HTML and have Vue render it as actual HTML. It's important to use v-html carefully, as it can expose your application to potential security risks, especially if the HTML content is user-generated.

<template>
  <p v-html="htmlContent"></p>
</template>

<script setup>
import { ref } from 'vue';

const htmlContent = ref('<strong>This is <em>dynamic</em> HTML content</strong>');
</script>

The v-html directive is employed to dynamically render HTML content. Within the script setup, a ref variable named htmlContent is declared, and initialized with a string containing HTML tags. The v-html directive is then applied to a <p> element in the template, binding it to the htmlContent variable. This allows Vue to interpret and render the HTML content dynamically.

Best Practices

Using v-once:

• For Static Content: Apply v-once to elements containing static content that remains unchanged.
• Performance Optimization: Use v-once strategically to improve rendering performance, especially in situations with a large number of static elements.

Using v-html:

• Sanitization: Be cautious when using v-html with user-generated content to prevent cross-site scripting (XSS) attacks. Sanitize the HTML content before binding it to ensure security. Sanitization involves inspecting and filtering the HTML content to ensure that it only contains safe and allowed elements, attributes, and properties.
• Avoid Dynamic Data: Minimize the use of v-html with dynamic data to reduce security risks.

Conclusion

With v-once, we can make sure that things that don't change, like titles and static content, are only calculated and displayed once for better performance. On the other hand, v-html lets us put dynamic HTML content in our pages, but we need to be careful with it, especially if users can input the HTML, to avoid security issues. So, whether we want to show something just once or include dynamic HTML, Vue.js has got us covered with these cool features!