为何jQuery的position()方法未提供Setter版本？

Great question! This is one of those jQuery design choices that clicks once you dig into what position() actually does under the hood. Let's break it down simply:

• position() returns a calculated, non-direct value
  Unlike offset()—which gives coordinates relative to the entire document and maps cleanly to setting an element's position—position() gives the offset of the element relative to its offset parent: the closest ancestor with a position value of relative, absolute, fixed, or sticky (if none exist, it defaults to the document body).

  This value isn't a direct reflection of the element's top/left CSS properties. For example, if an element uses the default position: static, changing its top/left styles won't affect its layout at all—so a position() setter would be completely useless here. Even for elements with non-static positioning, the position() value is a computed result of the element's styles and its parent's layout, not a single mutable property.

• A setter would introduce unnecessary complexity
  jQuery’s core philosophy is simplicity and predictability. To build a position() setter, the library would have to:

  1. Check if the element’s position CSS property even allows relative positioning.
  2. Account for dynamic changes to the offset parent’s layout or position.
  3. Handle edge cases like nested positioned elements, floating elements, or margin/padding altering the calculated position.

  All this complexity would outweigh the utility, especially since there are already straightforward ways to achieve the same goal.

• How to set a "position-like" value instead
  If you need to position an element relative to its parent, use these simple workarounds:

  1. Modify top/left directly with css()
     For elements with non-static positioning (e.g., relative or absolute), set their relative position like this:

     $('#myElement').css({ top: '20px', left: '30px' });
     

     For absolute elements, this positions them relative to their offset parent; for relative elements, it shifts them from their normal flow position.
  2. Calculate and use offset()
     For precise control relative to the parent, compute the parent’s offset and adjust accordingly:

     const parentOffset = $('#parent').offset();
     $('#myElement').offset({
       top: parentOffset.top + 20,
       left: parentOffset.left + 30
     });
     

内容的提问来源于stack exchange，提问作者Thor