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LoaderEvents Overview

In Yellowfin 9.4 we enabled the option to add customized loaders to the Javascript API through the “loaderEvents” API.

This allows a developer to listen for instances where an element within a Yellowfin element has a loader added to it or removed from it and then reacts to that event.

There are a number of different actions that could be taken. They include:

  • prevent the Yellowfin loader from being added, and add a custom loader onto the same element;
  • attach a loader to a different, related element; and.
  • log the loader being added or removed (useful during development).

For example, a business using a white-label version of Yellowfin software might prefer to use  their own loader icon to match their brand rather than the default blue circle that ships with Yellowfin.

Note: due to the nature of the LoaderEvents API, it has no properties nor events associated specifically with it.


Function Reference

yellowfin.loaderEvents

After the Yellowfin API init() call has completed, the yellowfin.loaderEvents function will become available. This provides two basic functions — listen and stopListening — which allow you to set  up and remove loader events as you require.  It also provides two functions that simplify replacing many child loaders at once — interceptChildLoadersForElement and stopListeningToElementIntercept.

listen(listenObject)

This creates a loader event listener with the passed listenObject object.

The listenObject object should contain the following parameters:

Parameter

Type

Description

Extra info

selector

String

The CSS selector for the object you wish to create the listener on. If you wish to intercept all loaders you can use the selector ‘html *’.

Either  selector or element must be defined to avoid an error that prevents the event listener from being created. Of the two, defining selector is preferable.

elementHTML Element

The HTML element to listen for loaders being added to. This will only trigger events if the element added to the loader to is the same as the element defined here.

Optional, as an alternative to defining selector.

onAdd

Function

The function that is called immediately before Yellowfin adds a loader to an element that matches the selector. A LoaderEvent will be passed to this callback function.

Either onAdd or onRemove must be defined. Both can be defined, if needed. If neither are defined, an error will be thrown and the event listener will not be created.

onRemove

Function

A callback function which is immediately before Yellowfin code removes a loader from an element that matches the selector. A LoaderEvent will be passed to this callback function.

Either onAdd or onRemove must be defined. Both can be defined, if needed. If neither are defined, an error will be thrown and the event listener will not be created.

stopListening(listenObject)

Removes a loader event, the passed listenObject must be the exact same object that was passed into the listen function. Otherwise the listener will not be removed.

interceptChildLoadersForElement(element, listenObject)

When this function is called, Yellowfin intercepts any elements with child loaders and applies those loaders to the passed element rather than the child. If interceptChildLoadersForElement is called multiple times on the same element, only the first application will be used.

The listenObject parameter for interceptChildLoadersForElement works in a similar manner to the listenObject parameter for loaderEvents.listen. The onAdd function will be called the first time a loader is added to the passed element, and onRemove will be called when the loader is removed from the passed element

In the sample code below, the code looks for loaders added anywhere on the page and adds them to the body tag instead.

yellowfin.loaderEvents.interceptChildLoadersForElement(document.querySelector('body'), {
    onAdd: function(e) { console.log('loader added to body') },
    onRemove: function(e) { console.log('loader removed from body') }
}); 

stoplisteningToElementIntercept (listenObject)

The interceptChildLoadersForElement() listener can be removed by using the stopListeningToElementIntercept() function .

Pass only the element you wish to stop listening to.

LoaderEvents.stopListeningToElementIntercept(document.querySelector('body'))

LoaderEvent

Each time an onAdd or onRemove function is called, a LoaderEvent object will be created. This contains the element the loader is going to be added to, as well as some functions which allow manipulation of how the event is handled.

LoaderEvent.element

This is the element which the loader is going to be added to or removed from. 

LoaderEvent.preventDefault()

This event prevents the loader from being added to or removed from the element. 

For example, you could initialize your event listener like this:

yellowfin.loaderEvents.listen({
    selector: ‘html *’,
    onAdd: function(event) {
        event.preventDefault();
    }
});

This would cause no loaders to be added to any Yellowfin elements. This by itself isn’t particularly useful, however you could combine the preventDefault with code that adds your own customized loader.

If you were to create an event listener that only contained an onRemove function that prevented default, like this:

yellowfin.loaderEvents.listen({
    selector: ‘html *’,
    onRemove: function(event) {
        event.preventDefault();
    }
});

This would prevent the loader from being removed from the element. As such you should generally only use preventDefault on removal when you are handling the loader removal yourself in the onRemove function.

LoaderEvent.setOverrideElement(element)

Defines an element to append the standard Yellowfin loader to, rather than the element that has been passed in the LoaderEvent object. 

This means that if you wish the standard Yellowfin loader to be on a parent element it can be. When using this function, you must define the setOverideElement in both the onAdd and onRemove functions.

yellowfin.loaderEvents.listen({
    selector: ‘report-output > div’, //Listen for loaders on immediate children of all reports
    onAdd: function(event) {
        event.setOverrideElement(event.element.parentNode); //Adds a loader to the parent node of the passed element
    }, 
    onRemove: function(event) {
        event.setOverrideElement(event.element.parentNode); //Removes the loader from the parent node
    }
});



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