Understanding the 'v-show' Directive in Vue.js

In Vue.js, the 'v-show' directive serves the purpose of toggling the visibility of an element. This powerful tool adds a simple yet effective dynamic behavior to your Vue application, allowing for elements to be shown or hidden based on the truthiness of the expression provided to the 'v-show' directive.

The 'v-show' directive functions by adding an inline CSS property 'display: none' to the element when the expression it's bound to evaluates to false. Therefore, although the element is invisible on the page, it does actually remain in the Document Object Model (DOM).

Let's look at an example:

<div v-show="isVisible">Hello, Vue!</div>

In this example, the div element containing the text "Hello, Vue!" will only be visible if the data property 'isVisible' is true. If 'isVisible' is false, the div will be hidden, but note, it is not removed from the DOM, just rendered invisible.

The 'v-show' directive differs from the 'v-if' directive, which physically inserts or removes elements from the DOM based on the truthiness of its expression, in terms of performance. Specifically, 'v-show' has better performance if the element is switched on and off frequently, while 'v-if' has better performance if the condition is unlikely to change at runtime.

The critical thing to remember about 'v-show' is that, although it makes the element invisible, it does not remove it from the DOM or stop it being rendered. This means any side effects of rendering the element, such as lifecycle hooks, will still be triggered, even if the element is not visible.

Despite 'v-show' having specific utility, it's essential to use it judiciously and understand all the nuances attached to it. Hence, understanding when to use it and when to opt for other alternatives like 'v-if' is simply a part of Vue’s power and flexibility.