Internal function used by the Tween Builder to create a function that will return the given value from the source.
| name | type | description |
|---|---|---|
| source | any |
The source object to get the value from. |
| key | string |
The property to get from the source. |
| defaultValue | any |
A default value to return should the source not have the property set. |
A function which when called will return the property value from the source.