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vue 1

vue

Conditional Rendering

v-if

In string templates, for example Handlebars, we would write a conditional block like this:

<!-- Handlebars template -->
{{#if ok}}
  <h1>Yes</h1>
{{/if}}

In Vue.js, we use the v-if directive to achieve the same:

<h1 v-if="ok">Yes</h1>

It is also possible to add an “else” block with v-else:

<h1 v-if="ok">Yes</h1>
<h1 v-else>No</h1>

Template v-if

Because v-if is a directive, it has to be attached to a single element. But what if we want to toggle more than one element? In this case we can use v-if on a <template> element, which serves as an invisible wrapper. The final rendered result will not include the <template> element.

<template v-if="ok">
  <h1>Title</h1>
  <p>Paragraph 1</p>
  <p>Paragraph 2</p>
</template>

v-show

Another option for conditionally displaying an element is the v-show directive. The usage is largely the same:

<h1 v-show="ok">Hello!</h1>

The difference is that an element with v-show will always be rendered and remain in the DOM; v-show simply toggles the display CSS property of the element.

Note that v-show doesn’t support the <template> syntax.

v-else

You can use the v-else directive to indicate an “else block” for v-if or v-show:

<div v-if="Math.random() > 0.5">
  Sorry
</div>
<div v-else>
  Not sorry
</div>

The v-else element must immediately follow the v-if or v-show element - otherwise it will not be recognized.

Component caveat

When used with components and v-show, v-else doesn’t get applied properly due to directives priorities. So instead of doing this:

<custom-component v-show="condition"></custom-component>
<p v-else>This could be a component too</p>

Replace the v-else with another v-show:

<custom-component v-show="condition"></custom-component>
<p v-show="!condition">This could be a component too</p>

It does work as intended with v-if.

v-if vs. v-show

When a v-if block is toggled, Vue.js will have to perform a partial compilation/teardown process, because the template content inside v-if can also contain data bindings or child components. v-if is “real” conditional rendering because it ensures that event listeners and child components inside the conditional block are properly destroyed and re-created during toggles.

v-if is also lazy: if the condition is false on initial render, it will not do anything - partial compilation won’t start until the condition becomes true for the first time (and the compilation is subsequently cached).

In comparison, v-show is much simpler - the element is always compiled and preserved, with just simple CSS-based toggling.

Generally speaking, v-if has higher toggle costs while v-show has higher initial render costs. So prefer v-show if you need to toggle something very often, and prefer v-if if the condition is unlikely to change at runtime.

© 2013–2017 Evan You, Vue.js contributors
Licensed under the MIT License.
https://v1.vuejs.org/guide/conditional.html