Prior to LockerService, when you created or obtained a reference to a component, you could call any function and access any property available on that component, even if it wasn’t public. When LockerService is enabled, components are “wrapped” by a new SecureComponent object, which controls access to the component and its functions and properties. SecureComponent restricts you to using only published, supported component API.
The reference doc app lists the API for SecureComponent. Access the reference doc app at:
https://<myDomain>.lightning.force.com/auradocs/reference.app, where <myDomain> is the name of your custom Salesforce domain.
The API for SecureComponent is listed at
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