append, prepend and replaceChildren insert null and undefined as the text "null" and "undefined"

Fact

append, prepend, before, after, replaceWith and replaceChildren take nodes or strings, and convert every argument that is not a node to a string. A conditional child written as cond ? el : null therefore adds a text node reading null (or undefined, false) instead of nothing.

Why it matters

Element helpers that skip null children train the habit of writing cond ? child : null; the same expression passed straight to a DOM method shows a stray "null" glued to the neighbouring text, often only in a rarely reached state.

How to apply

• Filter before calling: el.replaceChildren(...parts.filter((p) => p != null && p !== false)).
• Or route conditional children through the same helper that already drops them, and pass the DOM method a single built element.