simple and lightweight observer

Usage no npm install needed!

<script type="module">
  import obz from 'https://cdn.skypack.dev/obz';



A fork of https://github.com/dominictarr/obv

Represents a value changing in time.

Sometimes you have a sequence of values over time, usually we use streams for this. However, in some cases, the latest value, or the next value matters more than the entire history of values.

For example, if you are drawing the mouse pointer, you just need the current position, not the historical positions.

An observable is a simple way to represent these instantaniously changing values.

Obv() => observable

returns an observable instance.

observable(listener=function, immediate=boolean) => remove

register listener with the observable. immediate is true by default. listener is called with the current value (if one has been set), set to false to disable.

A function remove is returned, calling this function deregisters the listener.


set the current value of this observable. Any registered listeners will be called.

observable.once(listener=function, immediate=boolean) => remove

Like the above call to observable() except the listener will only be triggered once.

This is useful for representing variables which must be set after an async operation (say, initializing a database connection), but if the value is initalized you can act on it immediately.

If you call observable.once(listener, false) that triggers at the next time the value is set, which so far I have used to create live streams.


The current value of the observable is provided as a property. I recommend not using null as a observable value in your program, because it makes testing the current value awkward.