DOM Content Loaded (Start/End)

Collected from: Web Browser (API)

The DOMContentLoaded (DCL) is an event fired by the web browser. It has a start and an end as listeners can be attached at the event to trigger JavaScript execution when the event fires (that's basically what's jQuery.ready is doing). The DOMContentLoaded event fires when the initial HTML document has been completely loaded and parsed (without waiting for images, and iframes to finish loading).
Blocking JavaScript will delay the event. Make your JavaScript asynchronous to optimize DOMContentLoaded.

If DOMContentLoaded End is significantly higher than DOMContentLoaded Start, it means the page has listeners attached to this event triggering significant code execution and/or relying on network.

DOMContentLoaded Start immediately follows DOM Interactive. Between DOMInteractive and DCL Start, the only treatments are related to async scripts with a module type.

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