Managing Flow

You’ll often want to control the flow and frequency of concurrent operations. For example, you might not want to fire an ajax call until the user stops typing or you might only want to request the scroll position of a page after a certain period of time. Ency was built for these sort of operations in mind. Tasks have a flow modifier that you can use to manage the flow of repeat requests.

Task Flow

Default Behavior: Tasks Run Concurrently

By default, tasks run concurrently. In the demo below, notice how multiple calls to the same operation during the same period of time causes the lifespan of each one to overlap.

Most of the time you won’t want repeat calls to overlap, so you can use the flow modifier to specify policies and constraints for how repeat calls should be handled.

There are three options: you can either enqueue, restart, or drop repeat requests.


With task.flow('enqueue'), repeat calls are enqueued and only run when the previous call finishes.

In the demo below, notice how repeat calls do not overlap but all of them are eventually run to completion.


With task.flow('drop'), repeat calls are dropped and ignored.

In the demo below, notice how once the first instance starts running, all other calls during the same time period are never waited on or fired.


With task.flow('restart'), repeat calls cancel ongoing operations in favor of the newly created instance of the operation.

In the example below, notice how if a new instance is created during the same span of time, the older, ongoing instance is immediately canceled.

What if I want to run more than one instance at once?

The flow modifier takes a second parameter that allows you to configure additional options.

By default, any custom flow policy only allows one instance to run at a time. But you can increase the concurrency with the maxRunning option, which limits the number of instances allowed to run simultaneously.

Here’s an example with the enqueue policy:

task.flow('enqueue', { maxRunning: 3 })

Now, when you run the task, up to three instances are allowed to run at once while all others are scheduled to run when space frees up.

What if I want to delay the execution of the task?

To delay the execution of an operation, you can set the desired amount of time in delay option.

For example, if you wanted to simulate a debounce function, you could use the restart policy with a specified delay:

task.flow('restart', { delay: 400 })

Now, when you run the task, each instance waits 400ms before starting. If it’s called again within that time, then it’s dropped and not run at all, while another one is started in its favor.

How does this differ from throttle and debounce functions?

Ency buffers the execution of tasks using queues, while throttle and debounce functions use timers. The benefit of using queues, is that you always have access to the ongoing operations, which gives you more control over how repeat requests are run.

Another benefit of Ency’s flow policies is that their usage is more straightforward and semantic.