Snippet from Zepto.js, translated to CoffeeScript.

1-adjacency.js

var adjacencyOperators = {
  append: 'beforeEnd', 
  prepend: 'afterBegin', 
  before: 'beforeBegin', 
  after: 'afterEnd'
};

for (key in adjacencyOperators)
  $.fn[key] = (function(operator) {
    return function(html){
      return this.each(function(element){
        element['insertAdjacent' + (html instanceof Element ? 'Element' : 'HTML')](operator, html);
      });
    };
  })(adjacencyOperators[key]);

2-adjacency.coffee

adjacencyOperators = 
  append:  'beforeEnd' 
  prepend: 'afterBegin' 
  before:  'beforeBegin'
  after:   'afterEnd'

for key of adjacencyOperators
  $.fn[key] = (html) ->
    @each (element) ->
      element['insertAdjacent' + (if html instanceof Element then 'Element' else 'HTML')] operator, html

3-adjacency.generated.js

var adjacencyOperators, _fn;
adjacencyOperators = {
  append: 'beforeEnd',
  prepend: 'afterBegin',
  before: 'beforeBegin',
  after: 'afterEnd'
};
_fn = function(key) {
  return $.fn[key] = function(html) {
    return this.each(function(element) {
      return element['insertAdjacent' + (html instanceof Element ? 'Element' : 'HTML')](operator, html);
    });
  };
};
for (key in adjacencyOperators) {
  _fn(key);
}