$.ensure - Extending jQuery to guarantee passed in variable (of selector string, plain DOM element or jQuery instance) will be a jQuery instance without double wrapping it

gistfile1.txt

// double wrapping performance test: http://jsperf.com/check-jquery-wrap

$.extend({
  ensure: function(el) {
    return !(el instanceof jQuery) ? $(el) : el;
  }
});

// example use
function doSomethingWithEl(el) {
  el = $.ensure(el);
  el.addClass('someClass'); // we expect el to represent a jQuery instance here
}

var el;

// call it with a string selector
el = '.elClass';
doSomethingWithEl(el);

// call it with a dom element selector
el = document.getElementById('elId');
doSomethingWithEl(el);

// call it with jQuery if thats what we already have
el = document.getElementById('elId')
doSomethingWithEl(el);