How to use the @microsoft/teams-js.getContext function in @microsoft/teams-js

async componentDidMount() {
        microsoftTeams.initialize();
        microsoftTeams.getContext((context) => {
            this.userObjectId = context.userObjectId;
            // Initialize application insights for logging events and errors.
            this.appInsights = getApplicationInsightsInstance(this.telemetry, browserHistory);
            this.getCategory();
        });

    }

/* Initialize the Teams library before any other SDK calls.
             * Initialize throws if called more than once and hence is wrapped in a try-catch to perform a safe initialization.
             */

            microsoftTeams.initialize();
        }
        catch (e) {
        }
        finally {
            this.state = {
                groupId: null,
                upn: null
            };

            /** Pass the Context interface to the initialize function below */
            microsoftTeams.getContext(context => this.initialize(context as any));
        }
    }

public componentWillMount() {
        this.updateTheme(this.getQueryVariable("theme"));
        this.setState({
            fontSize: this.pageFontSize()
        });

        if (this.inTeams()) {
            microsoftTeams.initialize();
            microsoftTeams.registerOnThemeChangeHandler(this.updateTheme);
            microsoftTeams.getContext((context) => {
                this.setState({
                    entityId: context.entityId
                });
            });
        } else {
            this.setState({
                entityId: "This is not hosted in Microsoft Teams"
            });
        }
    }