Component gets blur event on launch if custom navigation params was set up.

[punksta]

you compare whole state here in _handleNavigationStateChange function

      const focused = state.routes[state.index] === this.props.navigation.state;

but if we use custom navigation params, these objects can be different.
so it's better to compare key.

      const focused = state.routes[state.index].key === this.props.navigation.state.key;

let's say we have component that sets custom params and receives screenArg from parent screen via navigation action :

    this.props.navigation.setParams({ customX: this._foo, customY: this.props.bar });

here is my console eval output when first visit of the component.

_this.props.navigation.state === state.routes[state.index] 
false

_this.props.navigation.state.key === state.routes[state.index].key
true

state.routes[state.index].params
Object {screenArg: Object, customX: function, customY: function}
_this.props.navigation.state.params
Object {screenArg: Object}

Keys are equals, but whole states are different and screen will have "blur" event on launch.