Conditional Rendering in Vue.js with 'v-if', 'v-else-if' and 'v-else' Directives

Vue.js offers a simple and effective solution for conditionally rendering elements in the DOM. The v-if, v-else-if, and v-else directives are the primary tools for achieving this.

Understanding 'v-if', 'v-else-if' and 'v-else'

The v-if directive in Vue.js is used to conditionally render a block. The block will only display if the directive’s expression returns a truthy value.

Here is an example:

<div v-if="isTrue">This will render when 'isTrue' is truthy</div>

The v-else-if and v-else directives are used together with v-if to create more complex conditional blocks.

<div v-if="value === 'A'">Value is A</div>
<div v-else-if="value === 'B'">Value is B</div>
<div v-else>Value is neither A nor B</div>

In this case, the second div will only render if the condition of v-if is false, and its own condition is true. If neither of those are true, the div with the v-else directive will render.

Best Practices

Don't forget, Vue.js conditionally renders elements, which means if the expression returns false, the element will not even exist in the rendered output's DOM. Therefore, if you need an element to remain in the DOM, but hidden, you should consider using v-show directive instead.

Also, Vue.js has a top-down, one-pass, non-look-ahead parser for directives. It simply executes the code line by line and doesn't look ahead for future conditions. So, always respect the order: v-if should be followed by v-else-if and finally v-else.

Lastly, overusing conditions could lead to more complex structures, making the code less readable and harder to maintain. Keep your templates as simple as possible and move complex logic to methods or compute properties.

In conclusion, the v-if, v-else-if, and v-else directives in Vue.js provide a powerful yet simple way to conditionally render elements, increasing your ability to create dynamic, responsive applications.