Got tired of using `if ($("#foo").length)`, so I wrote these helpers.

helpers.js

// Helpers
$.fn.isPresent = function() { return this && this.length > 0 }
$.fn.isBlank = function() { return typeof(this) == "undefined" || !this || (this && this.length == 0) }

// Examples
$("body").isPresent() // => true
$("#foo").isPresent() // => false
$("body").isBlank() // => false
$("#foo").isBlank() // => true

isBlank could be as simple as:

$.fn.isBlank = function() { return !this || !this.length }

Loose typing FTW!