This is the latest series of posts I am doing on a new Pluralsight course I created titled, “Communicate Between Salesforce Lightning Web Components”. You can also check out a free 10 minute preview video that explains how I got to this point in the post series.

Welcome Back

In the last post, I showed you a solution to display products, but only focused on how parent to child communication worked in that example. In this post, I will point out the portions of the code that involve working with an unrelated component and show you the unrelated component that displayProducts will be working with.

Just to refresh your memory, the code for displayProducts is as follows:

<!-- displayProduct.html -->

<template>
    <div class="slds-card slds-var-p-around_x-small">
        <lightning-input
            label="Search Key"
            type="text"
            onchange={handleSearchKeyChange}
            class="search-bar"
        ></lightning-input>
        <template if:true={products.data}>
          <template if:true={products.data.length}>
             <div class="content">
                <template for:each={products.data}
                     for:item="product">
                     <!-- Product Tile Component here-->
                     <c-product-tile
                        key={product.Id}
                        product={product}
                        onselected={handleProductSelected}
                        class="slds-var-m-around_x-small">
                     </c-product-tile>
                 </template>
              </div>
            </template>
            <template if:false={products.data.length}>
                <p>No products matching your selection</p>
            </template>
        </template>
        <template if:true={products.error}>
            <p>Error when getting product data</p>
        </template>
    </div>
</template>


// displayProducts.js

import { LightningElement, wire } from 'lwc';

import { publish, MessageContext } from 'lightning/messageService';
import PRODUCT_SELECTED_MESSAGE from '@salesforce/messageChannel/ProductSelected__c';

// getProducts() method in ProductController Apex class
import getProducts from '@salesforce/apex/ProductController.getProducts';

export default class DisplayProducts extends LightningElement {

    searchKey = '';     
    
    // Load context for Lightning Messaging Service 
    @wire(MessageContext) messageContext;

    //Publish ProductSelected message
    handleProductSelected(event) {  
        publish(this.messageContext, PRODUCT_SELECTED_MESSAGE, {
            productId: event.detail
        });
    }

    // Load the list of available products.
    @wire(getProducts, { searchKey: '$searchKey' })
    products;

    handleSearchKeyChange(event) {
        this.searchKey = event.target.value.toLowerCase();
    }

}

Notice in the code above that each productTile uses an onselected event to fire off the handleProductSelected function. Also notice that at the top of the JavaScript controller, publish and MessageContext functions are imported from lightning/messageService. These are required when working with Lightning Message Service (LMS).

Working with Lightning Message Service

Lightning Message Service (LMS) was introduced in Summer 20 and it offers a standard way to communicate across the DOM, or Document Object Model. LMS can be used with LWC’s, along with Aura components and even Visualforce pages – as long as they are contained within the same lightning page.

The Lightning App Page that is used to host the solution has two regions. displayProducts will be loaded into the left-hand region and on the right will be a new component named productCard.

When a user clicks a product tile in displayProducts, a message will be sent to the productCard component, allowing it to display additional detail information. Communicating with unrelated components allows a user to easily switch between the tiles and additional product information without having to navigate to an actual Salesforce detail page.

Steps to work with LMS:

1. Create a message channel.
2. Define scope of message channel.
3. Publish to the message channel.
4. Component that should receive data will subscribe to the message channel

Below is the code for the productCard component (which is the unrelated component in this example):

<!-- productCard.html -->

<template>
    <lightning-card icon-name="standard:apex_plugin">
        <template if:true={recordId}>
            <span slot="title">{productName}</span>
            <lightning-button-icon
                icon-name="utility:expand_alt"
                slot="actions"
                onclick={handleNavigateToRecord}
            ></lightning-button-icon>
            <div class="slds-var-m-horizontal_medium">
                <img
                    if:true={productPictureUrl}
                    src={productPictureUrl}
                    class="product"
                    alt="Product picture"
                />
                <lightning-record-view-form
                    record-id={recordId}
                    onload={handleRecordLoaded}
                    object-api-name="Product2"
                    density="compact"
                >
                    <lightning-output-field
                        field-name={familyField}
                    ></lightning-output-field>
                    <lightning-output-field
                        field-name={productCodeField}
                    ></lightning-output-field>
                    <lightning-output-field
                        field-name={msrpField}
                    ></lightning-output-field>
                    <lightning-output-field
                        field-name={descriptionField}
                    ></lightning-output-field>
                </lightning-record-view-form>
            </div>
        </template>
        <template if:false={recordId}>
            <div class="slds-var-p-around_large">
                <p class="placeholder">Select a product to see details</p>
            </div>
            
        </template>
    </lightning-card>
</template>

//  productCard.js

import { LightningElement, wire } from 'lwc';

// Lightning Message Service and a message channel
import { NavigationMixin } from 'lightning/navigation';
import { subscribe, MessageContext } from 'lightning/messageService';
import PRODUCT_SELECTED_MESSAGE from '@salesforce/messageChannel/ProductSelected__c';

// Utils to extract field values
import { getFieldValue } from 'lightning/uiRecordApi';

// Product__c Schema
import PRODUCT_OBJECT from '@salesforce/schema/Product2';
import NAME_FIELD from '@salesforce/schema/Product2.Name';
import PRODUCT_CODE_FIELD from '@salesforce/schema/Product2.ProductCode';
import FAMILY_FIELD from '@salesforce/schema/Product2.Family';
import MSRP_FIELD from '@salesforce/schema/Product2.MSRP__c';
import DESCRIPTION_FIELD from '@salesforce/schema/Product2.Description';
import PICTURE_URL_FIELD from '@salesforce/schema/Product2.Picture_URL__c';

/**
 * Component to display details of a Product__c.
 */
export default class ProductCard extends NavigationMixin(LightningElement) {
    // Exposing fields to make them available in template
    familyField = FAMILY_FIELD;
    msrpField = MSRP_FIELD;
    productCodeField = PRODUCT_CODE_FIELD;
    descriptionField = DESCRIPTION_FIELD;

    // Id of Product__c to display
    recordId;

    // Product fields displayed with specific format
    productName;
    productPictureUrl;

    /** Load context for Lightning Messaging Service */
    @wire(MessageContext) messageContext;

    /** Subscription for ProductSelected Lightning message */
    productSelectionSubscription;

    connectedCallback() {
        // Subscribe to ProductSelected message
        this.productSelectionSubscription = subscribe(
            this.messageContext,
            PRODUCT_SELECTED_MESSAGE,
            (message) => this.handleProductSelected(message.productId)
        );
    }

    handleRecordLoaded(event) {
        const { records } = event.detail;
        const recordData = records[this.recordId];
        this.productName = getFieldValue(recordData, NAME_FIELD);
        this.productPictureUrl = getFieldValue(recordData, PICTURE_URL_FIELD);
    }

    /**
     * Handler for when a product is selected. When `this.recordId` changes, the
     * lightning-record-view-form component will detect the change and provision new data.
     */
    handleProductSelected(productId) {
        this.recordId = productId;
    }

    handleNavigateToRecord() {
        this[NavigationMixin.Navigate]({
            type: 'standard__recordPage',
            attributes: {
                recordId: this.recordId,
                objectApiName: PRODUCT_OBJECT.objectApiName,
                actionName: 'view'
            }
        });
    }
}

Notice in the HTML code above (which is bolded), there is a lightning button icon component. If clicked the user will be directed to the products record page. This is just in case that is what the user would prefer to happen. Displaying the record detail information will be done using the lightning record view form base component, along with several output field base components.

Also notice in the Javascript code, import statements to access functions from the lightning message service, as well as the newly created message channel. The next import statement will include the uiRecordApi utility that allows me to extract field values for product fields, along with several import statements used to access schema metadata for specific Product2 fields.

Inside the class, I will begin by adding some local variables that will expose some of that schema metadata. Below that I need to define the scope of the message context, which in this case will just be the default of the active area. This is only available to me when using the @wire context.

Next is the handleRecordLoaded handler which is fired when the lightning record view form base component first loads. It will get the product record ID passed in the event message channel and use the uiRecordApi to extract the field values for the product name and picture URL.

The end result of this solution are two unrelated components that communicate seamlessly. The image below shows you what it looks like to have the components work together in a Lightning page for Experience Cloud.

The code and explanations in this post is just a sample of all that is covered in the Pluralsight course, “Communicate Between Salesforce Lightning Web Components”. Check that out if you are interested in learning more about how LWC’s communicate. You can also check out a free 10 minute preview video that explains how I got to this point in the post series.