Question

How do know width of an inline element, without adding to document?

With adding

var span = document.createElement('span');
span.innerHTML = 'Hello, world!';
span.offsetWidth; //0
document.body.appendChild(span);
span.offsetWidth; //70

How without adding to document?

Sorry for my english)

Answer 1

The width of an element does obviously depend on the styles used (e.g. on the font size), so it is impossible to compute the width of the element without knowing where it is in the DOM.

You may add it to some invisible element if you don’t want it to show on the screen.