Which is better, reflow or redraw?

Redrawing is more efficient than reflowing. If frequent reflow operations can be avoided, the performance of the page will be improved, because reflow is a relatively performance-consuming operation because it will cause the entire rendering tree to be rebuilt, while redrawing only requires redrawing elements to the page, and No need to recalculate the layout.

# Operating system for this tutorial: Windows 10 system, Dell G3 computer.

Reflow and repaint are two important processes when the browser renders the page.

Reflow refers to the process in which the browser needs to recalculate the layout of the elements and redraw the page when the size, position, etc. of the DOM elements change. Reflow is a relatively performance-intensive operation because it causes the entire render tree to be rebuilt.

Redrawing means that when the style of an element (such as color, background, etc.) changes, the browser only needs to redraw the element to the page without recalculating the layout. Compared with reflow, redrawing has less performance overhead.

So from a performance perspective, redrawing is more efficient than reflowing. If frequent reflow operations can be avoided, the performance of the page will be improved.

But in actual development, reflow and redrawing are difficult to completely avoid. Some operations (such as changing the size, position, style, etc.) of elements will inevitably cause reflow or redrawing. Therefore, when writing code, we need to minimize frequent reflow operations, which can be optimized in the following ways:

1. Use the transform property of CSS instead of top/left for position adjustment, because transform will not Trigger reflow.
2. Process DOM elements that require multiple operations offline, such as by setting their position attribute to absolute, and reinsert them into the document stream in one go after the operation is completed.
3. Using document fragments (DocumentFragment) for DOM operations can reduce the number of reflows.
4. Avoid using table layout, because table layout calculation usually requires more reflow operations.

In general, reasonably optimizing the code and minimizing the number of reflows and redraws can improve the performance and user experience of the page.

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