js/listener.md

Listener

A generator for proxy objects that run callbacks when properties are changed.

Interface

listener(target={})
// Creates a new proxy for target
listener.listen(prop, callback)
// Adds a callback on a property change
listener.listen([prop, ...], callback)
// Adds a callback to several properties at once
listener.listen(prop)
// Removes all callbacks from a given property

text(listener, "property")
// Returns a text node bound to listener.property
text(listener)
// Returns a text node proxy for the listener
text(listener).property
// Same as first example

When called with two arguments, this function returns a new text node that will automatically update to reflect the given property on the listener.

When called with only the listener, it creates a proxy object that, when indexed, returns the result of calling text on the listener and the indexed property name.

Note that repeatedly indexing the proxy will return a new text node each time.

bindContent(listener, "value")
// Returns a text node with listener.value as its content
// that will change whenever the value is changed
bindContent(listener, "value", html_element)
// Binds an existng HTML or Text node
bindContent(listener, "value", html_element, value => value.toUpperCase())
// Accepts a function to transform the value
bindContent(listener, "value", html_element, value => document.createElement("hr"))
// Also accepts HTML elements when the target is not a text node

This function may be removed in the future if it doesn't show any usefullnes that isn't already provided by the skooma bind function.

Example

import Listener from 'listener.js'
const listener = Listener({})

// Listen for any changed property
listener.listen("*", (value, prop) => console.log(`${prop} changed to ${value}`))

// Listen only for changes to the foo property
listener.listen("foo", prop => console.log("it was foo, by the way"))

// Several listeners for one property are possible
// They will be executed in order of definition
listener.listen("foo", prop => do_something())

listener.foo = "New Value"
// Triggers 3 handlers

listener.bar = "New Value"
// Triggers only the * handler