What is better in vue.js 2, use v-if or v-show?

tl;dr

Assuming the question is strictly about performance:

• v-show: expensive initial load, cheap toggling,
• v-if: cheap initial load, expensive toggling.

Evan You provided a more in depth answer at VueJS Forum

v-show always compiles and renders everything - it simply adds the "display: none" style to the element. It has a higher initial load cost, but toggling is very cheap.

Incomparison, v-if is truely conditional: it is lazy, so if its initial condition is false, it won't even do anything. This can be good for initial load time. When the condition is true, v-if will then compile and render its content. Toggling a v-if block actually tearsdown everything inside it, e.g. Components inside v-if are acually destroyed and re-created when toggled, so toggling a huge v-if block can be more expensive than v-show.

Short answer:

Use v-if if the condition won't change that often.

Use v-show if you want to toggle the condition more often.

Note: v-show does not remove the element from the DOM if your condition is false. So people can see it when they inspect your page.

Adding that usage of 'v-if' can have unexpected consequences, since it connects and disconnects elements from the DOM instead of modifying the elements' display.

For example, if you use it on a form and end up toggling that form off using v-if, you will receive this browser console warning:

    “Form submission canceled because the form is not connected”

If you use 'v-show', you won't encounter this problem.