什麼是前端開發中的viewport

viewport指代計算機圖形學上的多邊形(通常是矩形)，代表目前被viewed的區域，即目前位于使用者浏覽器内處于visible狀态的區域。Viewport之外的區域處于不可見狀态，直至其被scroll到viewport内為止。

A viewport represents a polygonal (normally rectangular) area in computer graphics that is currently being viewed. In web browser terms, it refers to the part of the document you’re viewing which is currently visible in its window (or the screen, if the document is being viewed in full screen mode). Content outside the viewport is not visible onscreen until scrolled into view.

參考文獻

Deferred loading is a technique that is used to postpone the rendering of CMS components. Any component that is outside the viewport (that is, the area that is visible to the user) is not rendered in advance.