Render Functions and Custom Component Options

Vue's render functions and custom component options offer a powerful way to dynamically generate and control the rendering of components.

For instance, you can conditionally render child components or slots based on certain criteria.

Here's a basic render function that conditionally renders slots:

return () => {
  const slots = useSlots();
  const children = [];

  if (props.val && slots.true) {
    children.push(slots.true());
  } else if (!props.val && slots.false) {
    children.push(slots.false());
  }

  return children;
};

Custom component options can be used to tag components with specific properties that can be checked during rendering. This is useful when you have a set of components and you want to treat some of them differently based on their role or type.

For example, you can define a custom option in a child component:

export default {
  props: ['if'],
  conditional: true, // Custom component option
  setup(props) {
    // ...
  },
};

And then in the parent component's render function, you can filter child components based on this custom option:

const slots = useSlots();
const conditionalComponents = slots
  .default()
  .filter((el) => el.type.conditional);

const children = [conditionalComponents];

This pattern is particularly useful when creating compound components that need to communicate and share state in a tightly coupled manner. It allows for a clean and declarative approach to rendering while maintaining flexibility and control over the component tree.