Request reloading

Request reloading in Alette Signal is a mounted request feature, allowing request blueprints to react to external changes by re-requesting the previously obtained data from the server.

Mounted reloading

Mounted reloading is a mounted request behaviour, allowing request blueprints to request data from the server by automatically calling the reload() function on .mount():

const getData = custom(
    runOnMount(),
	factory(() => true)
)

const { when } = getData.mount();

// No "execute()" invocation is needed.

when(({ isLoading }) => {
    if (isLoading) {
        console.log("Mounted reloading is active.")
	}
})

INFO

The runOnMount() middleware with no arguments is identical to runOnMount(true).

WARNING

Mounted reloading is enabled by default for the query request blueprint.

Disabling mounted reloading

To disable mounted reloading, pass the runOnMount() middleware to the request blueprint:

const getData = custom(
    runOnMount(false),
	/* ... */
)

const { when } = getData.mount();

when(({ isLoading }) => {
    if (isLoading) {
        // Never reached
        console.log("Mounted reloading is active.")
	}
})

Predicate-based mounted reload

To enable predicate-based mounted reload, pass a predicate function to the runOnMount() middleware:

const getData = custom(
    runOnMount(({ context }) => true),
    // or
    runOnMount(async ({ context }) => false),
)

DANGER

The runOnMount() predicate function is called once on request mount.

Reload control

To control request reloading, pass a predicate function to the reloadable() middleware:

let myNumber = 5;

const getData = custom(
    input(as<number>()),
    runOnMount(false),
    reloadable(({ prev, current }, { context }) => {
        if (!prev) {
            return true;
		}
        
        return prev.args < current.args;
	})
).using(() => ({ args: myNumber }))

const { reload } = getData.mount()

// Executed - no "prev" property is available for inspection yet.
// myNumber = 5
reload()

myNumber = 3

// Skipped - the "prev" property argument number is 
// higher than 3:
// prevMyNumber = 5
// myNumber = 3
reload()

myNumber = 10

// Executed - the "prev" property argument number is 
// lower than 10:
// prevMyNumber = 5
// myNumber = 10
reload()

TIP

The reloadable() middleware can accept async predicate functions:

custom(
    reloadable(
        async ({ prev, current }, { context }) => true
    )
)

How does reloading work?

1. The reload() function of a mounted request blueprint is called.
2. If the .using() method is configured, the bound request settings function is called, retrieving up-to-date request settings.
3. If the reload() function was called for the first time with the mounted reloading enabled, the reloadable() check is skipped and the server endpoint is called.
4. If a predicate function was not provided to the reloadable() middleware, and the input() middleware is absent, the server endpoint is called.
5. If a predicate function was provided to the reloadable() middleware, the predicate function is called:
   1. If the predicate function returns true, the server endpoint is called.
   2. If the predicate function returns false, the reloading is cancelled.
6. If the reloadable() middleware has no arguments, and the input() middleware is present, a deep equality argument check is performed:
   1. If the arguments are different, the server endpoint is called.
   2. If the arguments are identical, the reloading is cancelled.

INFO

A predicate function is a function that returns true or false.