Lightning Message Service (LMS) allow you to communicate between Visualforce and Lightning Components (Aura and LWC both) on any Lightning page. LMS API allow you to publish message throughout the lightning experience and subscribe the same message anywhere with in lightning page. https://nextsrini.blogspot.com/ https://www.youtube.com/channel/UCqIHkbuf1uGiN8QXwWX5dkQ

1. Salesforce Lightning Message Service
Lightning Message Service (LMS) is the Salesforce technology of its kind that facilitates
communication between Visualforce, Lightning Web Components, and Aura Components on
a Salesforce Lightning Page.
With the launch of LMS, Salesforce developers obtained a simple and seamless API for
publishing messages throughout the Lightning Experience platform and subscribed to
messages that originated from anywhere within Lightning Experience.
• In LWC we can access Lightning Message Channel with the scoped module
@salesforce/messageChannel.
• In Visualforce, we can use global variable $MessageChannel.
• In Aura, use lightning:messageChannel in your component
Create Lightning Message Channel
Currently we can create Lightning Message channel with Metadata API. You can create the
same with the help of VsCode.
You need to create one DX project then you need to place your message channel definition
with the suffix .messageChannel-meta.xml in the force-
app/main/default/messageChannels directory. like below folder structure.

2. Sample Message-meta.xml
<?xml version="1.0" encoding="UTF-8"?>
<LightningMessageChannel xmlns="https://soap.sforce.com/2006/04/metadata">
<masterLabel>Counter</masterLabel>
<isExposed>True</isExposed>
<lightningMessageFields>
<fieldName>operator1</fieldName>
</lightningMessageFields>
<lightningMessageFields>
<fieldName>constant1</fieldName>
</lightningMessageFields>
</LightningMessageChannel>
Import a Message Channel:
Here’s how to import a Lightning message channel that a component can use to
communicate via the Lightning Message Service.
// Syntax
import channelName from '@salesforce/messageChannel/channelReference';
// Syntax for resources in a managed package
import channelName from '@salesforce/messageChannel/namespace__channelReference';
// Example
import recordSelected from '@salesforce/messageChannel/Record_Selected__c';

3. channelName—An imported symbol that identifies the message channel.
channelReference—The API name of the message channel.
namespace—If the message channel is in a managed package, this value is the namespace
of the managed package. If the message channel is not in a managed package, do not
include a namespace.
Restrictions in LMS:
Here are several restrictions to the Lightning Message Service.
Under the following circumstances, you are unable to utilise LMS:
· Salesforce Mobile
· Communities
· AppExchange
Note:
LMS cannot be used to communicate with VF page contained in an iframe in Aura/LWC.
Examples of data that you can pass in a message include strings, numbers, booleans, and
objects. A message cannot contain functions and symbols.
The lightning:messageChannel component is only available in Lightning Experience.