Relay: unmask fragment by reading data from store

component.js

function itemTrackingHelper(relayContext, item) {
    const {title, description} = unmaskFragmentData({
        relayContext,
        relayData: item,
        fragmentPropName: 'item',
        fragment: itemTrackingHelperFragment
    });
}

const itemTrackingHelperFragment = graphql`
    fragment itemTrackingHelper_item on Item {
        title
        description
    }
`
class MyComponent extends React.Component {
    handleClick = e => {
        itemTrackingHelper(this.props.relay, this.props.item)
    }
    render() {
        return <a onClick={this.handleClick}>click here</a>;
    }
}

createFragmentContainer(MyComponent {
    item: graphql`
        fragment MyComponent_item on Item {
            ...itemTrackingHelper
        }
    `
});

unmaskFragmentData.js

import { getSelector } from 'relay-runtime';

export const unmaskFragmentData = ({ relayContext, relayData, fragmentPropName, fragment }) => {
    let fragmentFunc = fragment[fragmentPropName];
    if (typeof fragmentFunc === 'object') {
        fragmentFunc = fragmentFunc.modern; // compat mode
    }
    const selector = getSelector(relayContext.variables, fragmentFunc(), relayData);
    return relayContext.environment.lookup(selector).data;
};