What is the difference between v-if and v-show in Vue?

v-if and v-show are used for conditional rendering in Vue.js, but the mechanism is different. 1. v-if determines whether to insert or remove the DOM according to the conditions, which is suitable for scenarios where there is infrequent switching; 2. v-show is always retained in the DOM, and only controls visibility through the CSS display attribute, which is suitable for frequent switching; 3. Use v-if to save memory, while v-show provides smoother switching performance; 4. v-if is suitable for large chunks of content or delayed loading, and v-show is suitable for interactions that need to retain state; 5. v-if can be used in <template>, while v-show is incompatible with <template>. The initial rendering cost and switching efficiency should be weighed when choosing.

In Vue.js, both v-if and v-show are used to conditionally render elements, but they work in very different ways. Choosing the right one depends on your use case.

Rendering Behavior: The Core Different

The main difference between v-if and v-show lies in how they handle the DOM.

• v-if is conditional rendering . If the condition is false, the element isn't just hidden — it's completely removed from the DOM.
• v-show , on the other hand, simply toggles the CSS display property. The element stays in the DOM at all times, but becomes visible or invisible based on the condition.

This means that with v-if , there's more overhead when switching because Vue has to create or destroy elements. With v-show , the initial render cost is higher (since everything loads), but switching is faster.

When to Use v-if

Use v-if when:

• The condition doesn't change often.
• You want to save processing power when the block isn't needed.
• You're dealing with large sections of content that aren't always needed.

For example:

 <div v-if="isLoggedIn">
  Welcome back!
</div>

If a user isn't logged in, this block won't even exist in the DOM, which can help reduce memory usage.

A few tips:

• Avoid using v-if inside loops unless necessary.
• Consider wrapping conditional blocks in <template> when you need multiple elements.
• Be aware that components inside v-if will be re-mounted when the condition changes.

When to Use v-show

Use v-show if:

• The condition changes frequently.
• You need fast toggling without performance hiccups.
• The element needs to stay mounted for things like form state or animations.

An example:

 <div v-show="isVisible">
  This panel shows and hides quickly.
</div>

Since the element remains in the DOM, any input values or component state inside it will persist when toggling.

Some points to remember:

• Initial page load might be slower due to more DOM nodes.
• It's not compatible with <template> .
• It works best for simple show/hide interactions.

Performance Considerations

Performance differences matter depending on your app's behavior:

• Use v-if when rendering something once and leaving it alone.
• Use v-show when you expect frequent changes.

Also, keep in mind that v-if has better memory efficiency when things are off, while v-show gives smoother transitions when switching.

Summary

So, here's the deal:

• v-if removes elements from the DOM entirely.
• v-show just hides them with CSS.
• Pick v-if for rare toggles or big conditional blocks.
• Go with v-show when you toggle often and want smoothness over memory savings.

It's not complicated, but choosing the right directive can make a noticeable difference in performance and behavior.

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