Why Does jQuery\'s height() and width() Return Values for Hidden Elements?

jQuery: Hidden Elements and Dimension Properties

Contrary to the common assumption, elements with display:none do not always return 0 for jQuery's height() and width() methods. This deviation from expectations has been the subject of lingering confusion among programmers.

Unveiling the Mystery

The discrepancy arises from the way jQuery handles elements with the display:none style. When an element's offset width is 0, indicating that it's effectively hidden, jQuery attempts to determine its height using internal calculations:

1. Temporary Transformation: It temporarily modifies the element's CSS properties using jQuery.swap():

   • Sets position to "absolute"
   • Sets visibility to "hidden"
   • Sets display to "block"
2. Height Measurement: With these alterations, it obtains the height using getWidthOrHeight(...).
3. Property Restoration: Finally, it reverts the CSS properties to their previous values, effectively hiding the element again.

This entire process occurs seamlessly before the UI thread updates, preserving the element's hidden state while retrieving its dimensions. By making display:none elements accessible via height() and width(), jQuery ensures that computations involving their dimensions can be performed regardless of their visibility status.

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