Source: Alibaba cloud University - Developer class - Vue.js self study manual
Conditional judgement
v-if
Condition judgment uses v-if instruction:
v-if directive
Use the v-if directive in the element and template:
<!DOCTYPE html> <html> <head> <meta charset="utf-8"> <title>Vue Test case - Alicloud University(/edu.aliyun.com)</title> <script src="https://cdn.bootcss.com/vue/2.2.2/vue.min.js"></script> </head> <body> <div id="app"> <p v-if="seen">Now you see me</p> <template v-if="ok"> <h1>Alicloud University</h1> <p>What we learn is not only technology, but also dream!</p> <p>Ha ha what, typing hard!!!</p> </template> </div> <script> new Vue({ el: '#app', data: { seen: true, ok: true } }) </script> </body> </html>
Here, the v-if instruction determines whether to insert the p element based on the value of the expression seen (true or false).
In a string template, such as Handlebars, we have to write a conditional block like this:
<!-- Handlebars Template --> {{#if ok}} <h1>Yes</h1> {{/if}}
v-else
You can use the v-else instruction to add an "else" block to v-if:
v-else instruction
Randomly generate a number, judge whether it is greater than 0.5, and then output the corresponding information:
<!DOCTYPE html> <html> <head> <meta charset="utf-8"> <title>Vue Test case - Alicloud University(edu.aliyun.com)</title> <script src="https://cdn.bootcss.com/vue/2.2.2/vue.min.js"></script> </head> <body> <div id="app"> <div v-if="Math.random() > 0.5"> Sorry </div> <div v-else> Not sorry </div> </div> <script> new Vue({ el: '#app' }) </script> </body> </html>
Operation result
Sorry
v-else-if
v-else-if is added in 2.1.0. As the name implies, it is used as the else if block of v-if. It can be used many times in chain:
v-else instruction
Randomly generate a number, judge whether it is greater than 0.5, and then output the corresponding information:
<!DOCTYPE html> <html> <head> <meta charset="utf-8"> <title>Vue Test case - Alicloud University(edu.aliyun.com)</title> <script src="https://cdn.bootcss.com/vue/2.2.2/vue.min.js"></script> </head> <body> <div id="app"> <div v-if="type === 'A'"> A </div> <div v-else-if="type === 'B'"> B </div> <div v-else-if="type === 'C'"> C </div> <div v-else> Not A/B/C </div> </div> <script> new Vue({ el: '#app', data: { type: 'C' } }) </script> </body> </html>
V-else, v-else-if must follow v-if or v-else-if.
v-show
We can also use the v-show instruction to display elements according to conditions:
v-show instruction
<h1 v-show="ok">Hello!</h1>
Note: v-show does not support < template > syntax.
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