using-the-lazy-prop.md

Using the lazy Prop

One of the props of the <Fetch/> component is lazy. This determines whether or not a request will be made when the component mounts.

The default value of lazy depends on the request method being used.

Method	Default value
GET, HEAD, OPTIONS	false
POST, PUT, PATCH, DELETE	true

This is due to the way applications typically use these methods when performing reads and writes.

Read Requests

Read requests are frequently done as a result of the user navigating to some section of the page. For instance, if your application is for a library, and the user visits the URL /books/2, then you will likely want to kick off a request to fetch that book right after the page loads.

This is why lazy is false for GET requests.

Sometimes, APIs will use POST for read requests. In these situations, you will need to manually specify lazy as false if you would like to make the request when the component mounts.

Write Requests

Typically, write requests, such as updating or deleting a resource, are not done as the result of a user simply navigating to a page. Instead, these are typically performed when a user clicks a button to confirm the action.

This is why lazy is true for HTTP methods that typically refer to write requests.

Dynamic lazy prop usage

A neat pattern is to specify a dynamic lazy value based on some application state. For instance, consider a search page that serializes the user's search into a query parameter.

When the app loads, you may want to make the request immediately when the query parameter exists. But if there isn't a query parameter, then you won't want to make the request, because there's no search term to use in the request.

You can use a dynamic value for lazy to implement this behavior. The example below demonstrates how you might go about doing this.

<Fetch {...fetchProps} lazy={Boolean(params.search)}>
  {children}
</Fetch>