Tuesday 14 September 2021

Dynamic Interactions in Winter 22


If all goes according to plan, Dynamic Interactions go GA in Winter 22. The release notes have this to say about them:

With Dynamic Interactions, an event occurring in one component on a Lightning page, such as the user clicking an item in a list view, can update other components on the page.

Which I think is very much underselling it, as I'll attempt to explain in the rest of this post.

Sample App

You can find the code for the sample app at the Github repository. There's not a huge amount to it, you choose an Account and another component gets the Id and Name of the Account and retrieves the Opportunities associated with it:

Component Decoupling

What Dynamic Interactions actually allow us to do is assemble disparate components into custom user interfaces while retaining full control over the layout. The components can come from different developers, and we can add or remove components that interact with each other without having to update any source code, or with the components having the faintest idea about what else is on the page. 

This is something I've wanted for years, but was never able to find a solution that didn't require my custom components to know something about what was happening on the page.

The original way of providing a user with components that interact with each other was to create a container component and embed the others inside it. The container knows exactly which components are embedded, and often owns the data that the other components work on. There's no decoupling, and no opportunity to change the layout as you get the container plus all it's children or nothing. 

Lightning Message Service was the previous game changer, and that allowed components to be fairly loosely coupled. They would publish events when something happened to them, and receive events when something happened elsewhere that they needed to act on. They were still coupled through the messages that were sent and received though - any component that wished to participate had to know about the message channels that were in use and make sure they subscribed to and published on those. Good luck taking components developed by a third party and dropping those in to enhance your page. It did allow the layout to be easily changed and components, as long as they knew about the channels and messages, to be added and removed without changing any code. I was planning a blog post on this, but masterful inactivity has once again saved me the trouble of writing it then having to produce another post recommending against that approach 

With Dynamic Interactions, all that needs to happen is that components publish events when things of interest happen to them, and expose public properties that can be updated when things they should be interested in happen, the dream of decoupled components is realised.  The components don't have to listen for each other's events, that is handled by the lightning app builder page. As the designer of the page, I decide what should happen when a specific component fires a particular event fires. Essentially I use the page builder to wire the components to each other, through configuration.

Back to the Sample App

My app consists of two components (no container needed):

  • chooseAccount - this retrieves all the accounts in the system and presents the user with a lightning-combobox so they can pick one. In the screenshot above, it's on the left hand side. When the user chooses an account, an accountselected CustomEvent is fired with the details - all standard LWC:
                new CustomEvent(
                    {detail: {
                        recordId: this.selectedAccountId,
                        recordName: this.selectedAccountName
  • accountInfo - this retrieves the opportunity information for the recordId that is exposed as a public property, again all standard and, thanks to reactive properties, I don't have to manually take action when the id changes:
    @api get recordId() {
        return this._recordId;    

    set recordId(value) {
        if (value) {
    @wire(GetOpportunitiesForAccount, {accountId: '$_recordId'})
        if (result.data) {

and the final step is to use the Lightning App Builder to define what happens when the accountSelected event fires. I edit the page and click on the chooseAccount component, and there's a new tab next to the (lack of) properties that allows me to define interactions for the component - the Account Selected event:

and I can then fill in the details of the interaction:

In this case I'm targeting the accountInfo component and setting its public properties recordId and recordName to their namesakes from the published event. If I had additional components which cared about an account being selected, I'd create additional interactions to change their state to reflect the selection.

I now have two components communicating with each other, without either of them knowing anything about the other one, using entirely standard functionality. I can wire up additional components, move them around, or delete components at will.  


I regularly find myself producing is highly custom user interfaces that allow multiple records to be managed on a single page. For this use case, Dynamic Interactions are nothing short of a game changer, and I'm certain that this will be my go to solution. 


Friday 10 September 2021

JavaScript for Apex Programmers Part 1 - Typing


When I started working with Salesforce way back in 2008, I had a natural affinity for the Apex programming language, as I'd spent the previous decade working with Object Oriented languages - first C++, then 8 years or so with Java. Visualforce was also a very easy transition, as I had spent a lot of time building custom front ends using Java technologies - servlets first before moving on to JavaServer Pages (now Jakarta Server Pages), which had a huge amount of overlap with the Visualforce custom tag approach. 

One area where I didn't have a huge amount of experience was JavaScript. Oddly I had a few years experience with server side JavaScript due to maintaining and extending the OpenMarket TRANSACT product, but that was mostly small tweaks added to existing functionality, and nothing that required me to learn much about the language itself, such as it was back then. 

I occasionally used JavaScript in Visualforce to do things like refreshing a record detail from an embedded Visualforce page, Onload Handling or Dojo Charts. All of these had something in common though, they were snippets of JavaScript that were rendered by Visualforce markup, including the data that they operated on. There was no connection with the server, or any kind of business logic worthy of the name - everything was figured out server side. 

Then came JavaScript Remoting, which I used relatively infrequently for pure Visualforce, as I didn't particularly like striping the business logic across the controller and the front end, until the Salesforce1 mobile app came along. Using Visualforce, with it's server round trips and re-rendering of large chunks of the page suddenly felt clunky compared to doing as much as possible on the device, and I was seized with the zeal of the newly converted. I'm pretty sure my JavaScript still looked like Apex code that had been through some automatic translation process, as I was still getting to grips with the JavaScript language, much of which was simply baffling to my server side conditioned eyes. 

It wasn't long before I was looking at jQuery Mobile to produce Single Page Applications where maintaining state is entirely the job of the front end, which quickly led me to Knockout.js as I could use bindings again, rather than having to manually update elements when data changed. This period culminated my Dreamforce 2013 session on Mobilizing your Visualforce Application with jQuery Mobile and Knockout.js

Then in 2015, Lightning Components (now Aura Components) came along, where suddenly JavaScript got real. Rather than rendering via Visualforce or including from a static resource, my pages were assembled from re-usable JavaScript components. While Aura didn't exactly encourage it's developers down the modern JavaScript route, it's successor - Lightning Web Components - certainly did.

All this is rather a lengthy introduction to the purpose of this series of blogs, which are intended to (try to) explain some of the differences and challenges when moving to JavaScript from an Apex background. This isn't a JavaScript tutorial, it's more about what I wish I'd known when I started. It's also based on my experience, which as you can see from above, was a somewhat meandering path. Anyone starting their journey should find it a lot more straightforward now, but there's still plenty there to baffle!

Strong versus Weak (Loose) Typing

The first challenge I encountered with JavaScript was the difference in typing. 


Apex is a strongly typed language, where every variable is declared with the type of data that it can store, and that cannot change during the life of the variable. 

    Date dealDate;

In the line above, dealDate is declared of type Date, and can only store dates. Attempts to assign it DateTime or Boolean values explicitly will cause compiler errors:

    dealDate=true;         // Illegal assignment from Boolean to Date
    dealDate=System.now(); // Illegal assignment from DateTime to Date

while attempts to assign something that might be a Date, but turns out not to be at runtime will throw an exception:

    Object candidate=System.now();
    dealDate=(Date) candidate; // System.TypeException: Invalid conversion from runtime type Datetime to


JavaScript is a weakly typed language, where values have types but variables don't.  You simply declare a variable using var or let, then assign whatever you want to it, changing the type as you need to:

    let dealDate;
    dealDate=2;               // dealDate is now a number
    dealDate='Yesterday';     // dealDate is now a string
    dealDate=Date();          // dealDate is now a date

The JavaScript interpreter assumes that you are happy with the value you have assigned the variable and will use it appropriately. If you use it inappropriately, this will sometimes be picked up at runtime and a TypeError thrown. For example, attempting to run the toUpperCase() string method on a number primitive:

    let val=1;
    Uncaught TypeError: val.toUpperCase is not a function

However, as long as the way you are attempting to use the variable is legal, inappropriate usage often just gives you an unexpected result. Take the following, based on a simplified example of something I've done a number of times - I have an array and I want to find the position of the value 3.

    let numArray=[1,2,3,4];

which returns undefined, rather than the expected position of 2.

Did you spot the error? I used the square bracket notation instead of round brackets to demarcate the parameter. So instead of executing the indexOf function, JavaScript was quite happy to treat the function as an array and return me the third element, which doesn't exist.

JavaScript also does a lot more automatic conversion of types, making assumptions that might not be obvious.  To use the + operator as an example, this can mean concatenation for strings or addition for numbers, so there are a few decisions to be made:

lhs + rhs

1. If either of lhs/rhs is an object, it is converted to a primitive string, number or boolean

2. If either of lhs/rhs is string primitive, the other is converted to a string (if necessary) and they are concatenated

3. lhs and rhs are converted to numbers (if necessary) and they are added

Which sounds perfectly reasonable in theory, but can surprise you in practice:

    1 + true 

result: 2, true is converted to the number 1

    5 + '4'  

result '54', rhs is a string so 5 is converted to a string and concatenated.

    false + 2

result: 2, false is converted to the number 0

    5 + 3 + '5'

result '85' - 5 + 3 adds the two numbers to give 8, which is then converted to a string to concatenate with '5'

    [1992, 2015, 2021] + 9

result '1992,2015,20219' - lhs is an object (array) which is converted to a primitive using the toString method, giving the string '1992,2015,2021', 9 is converted to the string '9' and the two strings are concatenated

Which is Better?

Is this my first rodeo? We can't even agree on what strong and weak typing really mean, so deciding whether one is preferred over the other is an impossible task. In this case it doesn't matter, as Apex and JavaScript aren't going to change!

Strongly typed languages are generally considered safer, especially for beginners, as more errors are trapped at compile time. There may also be some performance benefits as you have made guarantees to the compiler that it can use when applying optimisation, but this is getting harder to quantify and in reality is unlikely to be a major performance factor in any code that you write.

Weakly typed languages are typically more concise,  and the ability to pass any type as a parameter to a function can be really useful when building things like loggers.

Personally I take the view that code is written for computers but read by humans, so anything that clarifies intent is good. If I don't have strong typing, I'll choose a naming convention that makes the type of my variables clear, and I'll avoid re-using variables to hold different types even if the language allows me to.