Detailed explanation of Vue.js conditional rendering
This article mainly shares with you the detailed explanation of Vue.js conditional rendering. In string templates, such as Handlebars, we have to write a conditional block like this:
<!-- Handlebars 模板 -->{{#if ok}} <h1 id="Yes">Yes</h1>{{/if}}
In In Vue, we use the v-if
directive to achieve the same function:
<h1 id="Yes">Yes</h1>
You can also use v-else
to add an "else block":
<h1 id="Yes">Yes</h1>No
# Use v-if
conditional rendering grouping on <template></template>
elements
becausev-if
is a directive, so it must be added to an element. But what if you want to switch multiple elements? At this time, you can treat a <template></template>
element as an invisible wrapping element, and use v-if
on it. The final rendering result will not contain <template></template>
elements.
<p id="example"> <template v-if='ok'> <h1 id="Title">Title</h1> <p>Paragraph 1</p> <p>Paragraph 2</p> </template></p>
var vm = new Vue({ el: '#example', data: { ok: true } })
#v-else
and v-else-if
can be used v-else
directive to represent an "else block" of v-if
:
<p v-if="Math.random() > 0.5"> Now you see me</p> <p v-else> Now you don't </p>
<p v-if="type === 'A'"> A </p> <p v-else-if="type === 'B'"> B </p> <p v-else-if="type === 'C'"> C </p> <p v-else> Not A/B/C </p>
v-else
The element must immediately follow the v-if
or v-else-if
after the element, otherwise it will not be recognized.
Similar to v-else
, v-else-if
must also be followed immediately by v-if
or v- after the element of else-if
.
v-show
Another option for showing elements based on conditions is the v-show
directive.
<h1 id="Hello">Hello!</h1>
The difference is that elements with v-show
will always be rendered and remain in the DOM. v-show
Simply toggle the element's CSS property display.
Note that v-show
does not support the <template></template>
element, nor does it support v-else
.
v-if vs v-show
v-if
is "real" conditional rendering, as it ensures that within the conditional block during the switch The event listeners and subcomponents are destroyed and recreated appropriately.
v-if
is also lazy: if the condition is false on initial rendering, nothing is done - rendering of the condition will not begin until the first time the condition becomes true piece.
In contrast, v-show
is much simpler - the element will always be rendered regardless of the initial conditions, and is simply toggled based on CSS.
Generally speaking, v-if
has higher switching overhead, while v-show
has higher initial rendering overhead. Therefore, if you need to switch very frequently, it is better to use v-show
; if the conditions rarely change at runtime, it is better to use v-if
.
v-if
In string templates, such as Handlebars, we have to write a conditional block like this:
<!-- Handlebars 模板 -->{{#if ok}} <h1 id="Yes">Yes</h1>{{/if}}
In Vue, we use v The -if
directive implements the same function:
<h1 id="Yes">Yes</h1>
You can also use v-else
to add an "else block":
<h1 id="Yes">Yes</h1>No
# in <template></template>
Use v-if
conditional rendering grouping on elements
Because v-if
is a directive, it must be It is added to an element. But what if you want to switch multiple elements? At this time, you can treat a <template></template>
element as an invisible wrapping element, and use v-if
on it. The final rendering result will not contain <template></template>
elements.
<p id="example"> <template v-if='ok'> <h1 id="Title">Title</h1> <p>Paragraph 1</p> <p>Paragraph 2</p> </template></p>
var vm = new Vue({ el: '#example', data: { ok: true } })
#v-else
and v-else-if
can be used v-else
directive to represent an "else block" of v-if
:
<p v-if="Math.random() > 0.5"> Now you see me</p> <p v-else> Now you don't </p>
<p v-if="type === 'A'"> A </p> <p v-else-if="type === 'B'"> B </p> <p v-else-if="type === 'C'"> C </p> <p v-else> Not A/B/C </p>
v-else
The element must immediately follow the v-if
or v-else-if
after the element, otherwise it will not be recognized.
Similar to v-else
, v-else-if
must also be followed immediately by v-if
or v- after the element of else-if
.
v-show
Another option for showing elements based on conditions is the v-show
directive.
<h1 id="Hello">Hello!</h1>
The difference is that elements with v-show
will always be rendered and remain in the DOM. v-show
Simply toggle the element's CSS property display.
Note that v-show
does not support the <template></template>
element, nor does it support v-else
.
v-if vs v-show
v-if
is "real" conditional rendering, as it ensures that within the conditional block during the switch The event listeners and subcomponents are destroyed and recreated appropriately.
v-if
is also lazy: if the condition is false on initial rendering, nothing is done - rendering of the condition will not begin until the first time the condition becomes true piece.
In contrast, v-show
is much simpler - the element will always be rendered regardless of the initial conditions, and is simply toggled based on CSS.
In general, v-if
has higher switching overhead, while v-show
has higher initial rendering overhead. Therefore, if you need to switch very frequently, it is better to use v-show
; if the conditions rarely change at runtime, it is better to use v-if
.
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