Fabien Taillon, Partner & CTO at Texeï fabien@texei.com Dynamic Lightning Web Components With great power comes great responsibility

Fabien Taillon Partner & CTO at Texeï Salesforce MVP - Hall of Fame Paris Developer Group leader French Touch Dreamin team https://www.texei.com/blog

Introduction

What is a Dynamic Component A way to dynamically instantiate a component that may not be known before runtime @FabienTaillon - https://www.texei.com/blog

Why was This Not Possible Before? @FabienTaillon - https://www.texei.com/blog

Why was This Not Possible Before? PERFORMANCE @FabienTaillon - https://www.texei.com/blog

We have purposely made the decision of not allowing dynamic component creation yet (the equivalent of $A.createComponent) on the Salesforce platform to make sure we had a clean, statically analyzable and predictable behavior on which to build upon in LWC. … In LWC in the platform we don't allow you to shoot yourself in the foot creating small tiny components, and once we do, we will give you a water pistol first :) Diego Ferreiro Val - Ex Principal Architect LWC https://salesforce.stackexchange.com/questions/244847/not-able-to-render-dynamic-lightning-web-component

Valid use cases Most use cases can be achieved with existing lwc:if/lwc:elseif, but: • N°1 use case would be for AppExchanges allowing dynamic components defined through Metadata for instance (think App Builder like) • Can be used to defer big components load if not on the main displayed page • Displayed after a button click • Displayed in another tab • … @FabienTaillon - https://www.texei.com/blog

How it works now Just add the capability to the parent component to instantiate dynamic components: 59.0 lightning__dynamicComponent @FabienTaillon - https://www.texei.com/blog

How It Works Now And then it’s very easy: • Import component in JS • import MyComponent from 'c/myComponent'; • await import('c/myComponent'); • Define a Dynamic component in template with lwc:component and lwc:is • • Assign in JS the component you want to render • this.componentConstructor = MyComponent; @FabienTaillon - https://www.texei.com/blog

Pass Attributes Down Easily pass attributes via markup Depending on dynamic components, you may not know which attributes are need. Properties can be passed down via JavaScript object and lwc:spread directive: JS childProps = { city: "San Francisco", state: "CA" }; Markup @FabienTaillon - https://www.texei.com/blog

A Deeper Look

Before Dynamic Components Declarative use of components in the template markup All components are known at save time and can be statically analyzed @FabienTaillon - https://www.texei.com/blog

Before Dynamic Components Only one round trip to get the whole component and sub-components @FabienTaillon - https://www.texei.com/blog c-my-component c-my-component + c-small-component + c-heavy-component

With Dynamic Components Dynamic components will be created by JS and may not be known at that time Depends on how dynamic components are created - more on this later @FabienTaillon - https://www.texei.com/blog

With Dynamic Components If not done correctly, one additional round trip per dynamic component @FabienTaillon - https://www.texei.com/blog c-my-component c-my-component + c-small-component c-heavy-component c-heavy-component

Dynamic Components To do it correctly, you need to understand how it works and different options available @FabienTaillon - https://www.texei.com/blog

Static Import - Statically Analyzable ● Import needed components ● Switch the rendered component by changing the lwc:is variable ● Almost the same as using components in markup and lwc:if ● Everything is downloaded with a single server round trip @FabienTaillon - https://www.texei.com/blog

Dynamic Import - Statically Analyzable ● Same as previous, but loading is done on demand ○ connectedCallback ○ Function linked to any action (user click…) ● Not part of the initial load so additional server round trip @FabienTaillon - https://www.texei.com/blog

Dynamic Import - Not Statically Analyzable ● Same as previous BUT component is not statically analyzable ● No way for Salesforce to improve loading, caching etc ● As much as possible, don’t use this one @FabienTaillon - https://www.texei.com/blog

A Good Use Case

Loading Heavy Component Async ● One heavy component ● Not visible during first page load ● Would slow down the whole page if part of the markup @FabienTaillon - https://www.texei.com/blog

Loading Heavy Component Async @FabienTaillon - https://www.texei.com/blog

Recap

Recap ● Use it when you understand how it works ● Not for very small components, server round trip will be slower than initial load ● Use it for big components that may slow down initial load and that are not immediately visible (like unclicked tab) @FabienTaillon - https://www.texei.com/blog

Resources Documentation https://developer.salesforce.com/docs/platform/lwc/guide/js- dynamic-components.html Blog post https://developer.salesforce.com/blogs/2023/10/dynamic-co mponents-for-lightning-web-components-is-now-ga RFC https://github.com/jmsjtu/lwc-rfcs/blob/jtu/dynamic-compon ent-creation/text/0119-dynamic-component-creation.md StackExchange answer about performance https://salesforce.stackexchange.com/questions/244847/not- able-to-render-dynamic-lightning-web-component @FabienTaillon - https://www.texei.com/blog

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