Hi in the following function, what dos the question mark mean:
static getCurrentAccessToken(callback: (token: ?FBSDKAccessToken) => void) {
FBSDKAccessTokenInterface.getCurrentAccessToken((tokenDict) => {
callback(tokenDict ? new FBSDKAccessToken(tokenDict) : null);
});
}
I dont understand this part: (token: ?FBSDKAccessToken)
And yes, this is javascript ES6. Have a look here. Update: this is flow handling javascript.