Html element size when not visble?

Question

do elements before they are part of the dom have the width and height set properly? ie if I create a div containing markup can I measure its intended width and height without appending it to the dom?

Answer 1

I don't formally know the answer, but a little gedankenexperiment lets us see that it can't, in general, happen. If you create an HTML element with a fixed width and height, then yes - you can know the width and height.

However, if you don't specify them (or they might not be obeyed), then the width and height are always going to be calculated by the contextual position of the fragment in the DOM; for example, a DIV with width: 50% cannot know it's actual width until it is added to the DOM and laid out - there's no other way to answer "50% of what?".