# CallbackProperty

#### new Cesium.CallbackProperty(callback, isConstant)
engine/Source/DataSources/CallbackProperty.js 15

A `Property` whose value is lazily evaluated by a callback function.

Name | Type | Description
--- | --- | ---
`callback` | CallbackProperty.Callback | The function to be called when the property is evaluated.
`isConstant` | boolean | `true` when the callback function returns the same value every time, `false` if the value will change.

### Members

#### readonly definitionChanged : Event
engine/Source/DataSources/CallbackProperty.js 43

Gets the event that is raised whenever the definition of this property changes. The definition is changed whenever setCallback is called.

#### readonly isConstant : boolean
engine/Source/DataSources/CallbackProperty.js 30

Gets a value indicating if this property is constant.

### Methods

#### equals(other) → boolean
engine/Source/DataSources/CallbackProperty.js 100

Compares this property to the provided property and returns `true` if they are equal, `false` otherwise.

Name | Type | Description
--- | --- | ---
`other` | Property | optional The other property.

##### Returns:

`true` if left and right are equal, `false` otherwise.

#### getValue(time, result) → object
engine/Source/DataSources/CallbackProperty.js 59

Gets the value of the property.

Name | Type | Default | Description
--- | --- | --- | ---
`time` | JulianDate | `JulianDate.now()` | optional The time for which to retrieve the value. If omitted, the current system time is used.
`result` | object |  | optional The object to store the value into, if omitted, a new instance is created and returned.

##### Returns:

The modified result parameter or a new instance if the result parameter was not supplied or is unsupported.

#### setCallback(callback, isConstant)
engine/Source/DataSources/CallbackProperty.js 72

Sets the callback to be used.

Name | Type | Description
--- | --- | ---
`callback` | CallbackProperty.Callback | The function to be called when the property is evaluated.
`isConstant` | boolean | `true` when the callback function returns the same value every time, `false` if the value will change.

### Type Definitions

#### Cesium.CallbackProperty.Callback(time, result) → object
engine/Source/DataSources/CallbackProperty.js 109

A function that returns the value of the property.

Name | Type | Default | Description
--- | --- | --- | ---
`time` | JulianDate | `JulianDate.now()` | optional The time for which to retrieve the value. If omitted, the current system time is used.
`result` | object |  | optional The object to store the value into. If omitted, the function must create and return a new instance.

##### Returns:

The modified result parameter, or a new instance if the result parameter was not supplied or is unsupported.

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