---
id: fast-element.observable
title: Observable variable
hide_title: true
---
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[@microsoft/fast-element](./fast-element.md) &gt; [Observable](./fast-element.observable.md)

## Observable variable

Common Observable APIs.

<b>Signature:</b>

```typescript
Observable: Readonly<{
    setArrayObserverFactory(factory: (collection: any[]) => Notifier): void;
    getNotifier: (source: any) => Notifier;
    track(source: unknown, propertyName: string): void;
    trackVolatile(): void;
    notify(source: unknown, args: any): void;
    defineProperty(target: {}, nameOrAccessor: string | Accessor): void;
    getAccessors: (target: {}) => Accessor[];
    binding<TSource = any, TReturn = any, TParent = any>(binding: Binding<TSource, TReturn, TParent>, initialSubscriber?: Subscriber | undefined, isVolatileBinding?: boolean): BindingObserver<TSource, TReturn, TParent>;
    isVolatileBinding<TSource_1 = any, TReturn_1 = any, TParent_1 = any>(binding: Binding<TSource_1, TReturn_1, TParent_1>): boolean;
}>
```