When do DOM Elements Trigger Reflow?

When Does Reflow Occur in a DOM Environment?

Reflow is a process in a DOM environment that recalculates the layout and position of elements. Determining when reflow occurs is crucial for optimizing JavaScript performance.

Types of Activities That Trigger Reflow

There are two primary sources that describe reflow triggers:

1. Nczonline.net states that reflow occurs when:

   • Adding or removing DOM nodes
   • Applying styles dynamically
   • Retrieving measurements (e.g., offsetWidth, clientHeight, computed CSS values)
2. Opera.com suggests that measurements trigger reflow only when reflow is already queued.

Reconciling the Differences

However, both articles essentially agree that any action that requires the calculation of element dimensions can trigger reflow. This includes:

• Inserting or Deleting DOM Nodes: Adding or removing nodes alters the layout and requires reflow to update positions.
• Applying Dynamic Styles: Changing styles via element.style.width also influences the layout and triggers reflow.
• Measurement Retrieval: Accessing measurements like offsetWidth or computed CSS values forces a reflow operation to obtain the correct dimensions.

Conclusion

To ensure optimal performance, assume that any activity that reasonably necessitates the calculation of DOM element dimensions will likely trigger reflow. By understanding these triggers, developers can optimize their JavaScript code by minimizing reflows, cacheing values, or using other techniques that reduce the impact on DOM recalculation.

The above is the detailed content of When do DOM Elements Trigger Reflow?. For more information, please follow other related articles on the PHP Chinese website!