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Dynamic LWC With great power comes great responsibility

Fabien Taillon - Salesforce MVP - Hall of Fame - Paris Developer Group leader - French Touch Dreamin team - https://x.com/FabienTaillon - https://www.linkedin.com/in/fabientaillon - https://trailblazer.me/id/fabien - https://texei.com/blog Partner & CTO

Introduction

What is a Dynamic Component A way to instantiate dynamically a component that may not be known before runtime

Why it was not possible before

Why it was not possible before Performance

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 ○ …

How it works now 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;

A deeper look

Declarative use of components in the template markup All components are known at save time and can be statically analyzed Before Dynamic Components

Before Dynamic Components c-my-component Only one round trip to get the whole component and sub-components 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

With Dynamic Components c-my-component If not done correctly, one additional round trip per dynamic 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

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

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

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

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

Loading heavy component async

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)

Resources Documentation https://developer.salesforce.com/docs/platform/lwc/guide/js-dynamic-components.html Blog post https://developer.salesforce.com/blogs/2023/10/dynamic-components-for-lightning-web-c omponents-is-now-ga RFC: https://github.com/jmsjtu/lwc-rfcs/blob/jtu/dynamic-component-creation/text/0119-dyna mic-component-creation.md StackExchange answer about performance https://salesforce.stackexchange.com/questions/244847/not-able-to-render-dynamic-light ning-web-component

Q&A

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