Salesforce LWC Life Cycle Overview 2. This is the lifecycle of a component instance and its children from creation through render. constructor () is called. Public properties are updated. Component is inserted into the DOM. connectedCallback () is called. Component is rendered. constructor () is called on child components. 2 Answers. Accessing assignedNodes or assignedElements on a <slot> is the canonical way to verify if it has slotted content. In the case of modal with a header, for example, the component needs to handle the case where a slotted content is added or removed. Relying on the renderedCallback is not enough in this case since there is no guaranty. Salesforce has countless one-off issues like this, but my understanding is LWCs are supposed to be an open source framework, not coupled to Salesforce's infrastructure Maybe I just need to learn the API better.