[jquery] How to position one element relative to another with jQuery?

Here is a jQuery function I wrote that helps me position elements.

Here is an example usage:

$(document).ready(function() {
  $('#el1').position('#el2', {
    anchor: ['br', 'tr'],
    offset: [-5, 5]
  });
});

The code above aligns the bottom-right of #el1 with the top-right of #el2. ['cc', 'cc'] would center #el1 in #el2. Make sure that #el1 has the css of position: absolute and z-index: 10000 (or some really large number) to keep it on top.

The offset option allows you to nudge the coordinates by a specified number of pixels.

The source code is below:

jQuery.fn.getBox = function() {
  return {
    left: $(this).offset().left,
    top: $(this).offset().top,
    width: $(this).outerWidth(),
    height: $(this).outerHeight()
  };
}

jQuery.fn.position = function(target, options) {
  var anchorOffsets = {t: 0, l: 0, c: 0.5, b: 1, r: 1};
  var defaults = {
    anchor: ['tl', 'tl'],
    animate: false,
    offset: [0, 0]
  };
  options = $.extend(defaults, options);

  var targetBox = $(target).getBox();
  var sourceBox = $(this).getBox();

  //origin is at the top-left of the target element
  var left = targetBox.left;
  var top = targetBox.top;

  //alignment with respect to source
  top -= anchorOffsets[options.anchor[0].charAt(0)] * sourceBox.height;
  left -= anchorOffsets[options.anchor[0].charAt(1)] * sourceBox.width;

  //alignment with respect to target
  top += anchorOffsets[options.anchor[1].charAt(0)] * targetBox.height;
  left += anchorOffsets[options.anchor[1].charAt(1)] * targetBox.width;

  //add offset to final coordinates
  left += options.offset[0];
  top += options.offset[1];

  $(this).css({
    left: left + 'px',
    top: top + 'px'
  });

}