Report this

What is the reason for this report?

Conditional Directives With Vue.js

Published on December 16, 2016
Conditional Directives With Vue.js

The ability to show or hide elements based on conditions is a fundamental feature of any frontend framework. Vue.js provides us with a set of core directives to achieve this effect: v-if, v-else, v-else-if and v-show.

After getting started with a Vue.js Hello World application, we can use values from JavaScript data object to conditionally control the view. For example, we’ll see how to use the simple data object given below.

data() {
  return {
    msg: "Hello World!",
    isLoggedIn: false
  }
}

v-if

The v-if directive adds or removes DOM elements based on the given expression.

We can use the isLoggedIn property from the data model and show a login button in the view.

<button v-if="isLoggedIn">Logout</button>

Now, the button will not show because isLoggedIn is set to false. Setting the data.isLoggedIn value to true would add the button to the DOM.

<template> element

The v-if directive can only show or hide one element (and its child elements), but you can also control multiple elements with a single v-if reducing duplication.

To do this, you need to wrap all the elements that should be controlled by this condition in a <template> element. The template element itself will not be added to the DOM. But all containing elements will be added or removed depending on the v-if expression.

For example, if you need to show a label as well as a button when the isLoggedIn is true you can wrap both elements in a single template element as follows.

<template v-if="isLoggedIn">
  <label> Logout </button>
  <button> Logout </button>
</template>

v-else

As the name v-else suggests, this directive is used to display content only when the expression adjacent v-if resolves to false.

We can have a Log In button to show automatically when the isLoggedIn is false.

<button v-if="isLoggedIn"> Logout </button>
<button v-else> Log In </button>

v-else does not need a value passed in to it. But it must be in an element that comes immediately after an element containing v-if or v-else-if directives.

v-else-if

v-else-if can be used when we need more than two options to be checked. This will ensure that only one of the chained items in the else-if chain will be visible.

For example, if the property named isLoginDisabled is true, we can prevent the Log In button from displaying and instead display a label. We can accomplish it by using the v-else-if directive as follows.

<button v-if="isLoggedIn"> Logout </button>
<label v-else-if="isLoginDisabled"> Register disabled </label>
<button v-else> Log In </button>

v-show

Very similar to v-if, the v-show directive can also be used to show and hide an element based on an expression.

The main difference between the two is that,

  • v-if - Only renders the element to the DOM if the expression passes.
  • v-show - Renders all elements to the DOM and then uses the CSS display property to hide elements if the expression fails.
  • v-show - Does not support v-else, v-else-if

Usually, v-show has a performance advantage if the elements are switched on and off frequently, while the v-if has the advantage when it comes to initial render time.

Thanks for learning with the DigitalOcean Community. Check out our offerings for compute, storage, networking, and managed databases.

Learn more about our products

About the author

Alligator
Alligator
Author
See author profile

Alligator.io is a developer-focused resource that offers tutorials and insights on a wide range of modern front-end technologies, including Angular 2+, Vue.js, React, TypeScript, Ionic, and JavaScript.

Category:
Tags:
While we believe that this content benefits our community, we have not yet thoroughly reviewed it. If you have any suggestions for improvements, please let us know by clicking the “report an issue“ button at the bottom of the tutorial.

Still looking for an answer?

Was this helpful?


This textbox defaults to using Markdown to format your answer.

You can type !ref in this text area to quickly search our full set of tutorials, documentation & marketplace offerings and insert the link!

Creative CommonsThis work is licensed under a Creative Commons Attribution-NonCommercial- ShareAlike 4.0 International License.
Join the Tech Talk
Success! Thank you! Please check your email for further details.

Please complete your information!

The developer cloud

Scale up as you grow — whether you're running one virtual machine or ten thousand.

Get started for free

Sign up and get $200 in credit for your first 60 days with DigitalOcean.*

*This promotional offer applies to new accounts only.