Parcel meta

Parcel meta provides the ability to store extra data that pertains to parts of a data shape, such as validation error messages against each of the fields in a form. Each location (unique key path) in a Parcel’s value has a corresponding meta object, which defaults to an empty object.

let parcel = new Parcel({
    value: {
        abc: 123,
        def: {
            ghi: 456
        }
    }
});

// the value above has four locations where meta can be stored:
parcel.meta // returns the meta data object on the top level parcel
parcel.get('abc').meta // returns the meta data object at ['abc']
parcel.get('def').meta // returns the meta data object at ['def']
parcel.get('def').get('ghi').meta // returns the meta data object at ['def', 'ghi']

There are three main ways to interact with meta on a Parcel:

Meta is set using a Parcel’s setMeta() method, which triggers a change that sets meta at the parcel’s location.

let parcel = new Parcel({
    value: "abc"
});

parcel.setMeta({
    abc: 123
});
// ^ this triggers a change that sets the parcel's meta to {abc: 123}

parcel.setMeta({
    def: 456
});
// ^ this triggers a change that sets the parcel's meta to {abc: 123, def: 456}

The initialMeta() method can also be used to set the initial meta object.

let parcel = new Parcel({
    value: "abc"
});

parcel
    .initialMeta({
        abc: 123
    })
    .meta // this returns {abc: 123} initially, but this can change after subsequent calls to setMeta()

Examples

See the confirmation and selections examples to see how meta can be used.

Displaying changed values

Additionally, this example shows how meta and initialMeta() can be used to store information in meta for later reference.

Changed? No
Changed? No
personParcel
{
    "firstname": "Robert",
    "lastname": "Clamps"
}
import React from 'react';
import useParcelState from 'react-dataparcels/useParcelState';
import ParcelBoundary from 'react-dataparcels/ParcelBoundary';

const withOriginalMeta = (parcel) => parcel.initialMeta({
    original: parcel.value
});

export default function PersonEditor(props) {

    let [personParcel] = useParcelState({
        value: {
            firstname: "Robert",
            lastname: "Clamps"
        }
    });

    let firstname = personParcel
        .get('firstname')
        .pipe(withOriginalMeta);

    let lastname = personParcel
        .get('lastname')
        .pipe(withOriginalMeta);

    return <div>
        <label>firstname</label>
        <ParcelBoundary parcel={firstname}>
            {(firstname) => <div>
                <input type="text" {...firstname.spreadDOM()} />
                <div>Changed? {firstname.meta.original === firstname.value ? 'No' : 'Yes'}</div>
            </div>}
        </ParcelBoundary>

        <label>lastname</label>
        <ParcelBoundary parcel={lastname}>
            {(lastname) => <div>
                <input type="text" {...lastname.spreadDOM()} />
                <div">Changed? {lastname.meta.original === lastname.value ? 'No' : 'Yes'}</div>
            </div>}
        </ParcelBoundary>
    </div>;
}

What’s going on

  • The firstname and lastname parcels use the pipe() method, which simply passes each parcel through the withOriginalMeta function and calls the initialMeta() function on each of them.
  • initialMeta() gets the initial value of the parcel and stores it in meta.original
  • When rendering, meta.original is compared against the current value to detect changes of the value since the initial render.