polymer Polymer Cheat Sheet Observers
Example
Docs: observers, multi-property observers, observing array mutations, adding observers dynamically.
Adding an observer in the properties block lets you observe changes in the
value of a property:
static get properties() {
return {
myProperty: {
observer: '_myPropertyChanged'
}
}
}
// The second argument is optional, and gives you the
// previous value of the property, before the update:
_myPropertyChanged(value, /*oldValue */) { /* ... */ }
In the observers block:
static get observers() {
return [
'_doSomething(myProperty)',
'_multiPropertyObserver(myProperty, anotherProperty)',
'_observerForASubProperty(user.name)',
// Below, items can be an array or an object:
'_observerForABunchOfSubPaths(items.*)'
]
}
Adding an observer dynamically for a property otherProperty:
// Define a method.
_otherPropertyChanged(value) { /* ... */ }
// Call it when `otherPropety` changes.
this._createPropertyObserver('otherProperty', '_otherPropertyChanged', true);
