Proper (according to me) "contains" method for arrays in javascript. This allows the use of callback on testing.

Array.prototype.isPresent.js

/**
 * Proper (according to me) "isPresent" method for arrays in javascript. This allows the use of callback on testing.
 * An empty callback is like using '==' as test.
 * @param item item to find
 * @param cpf -optional- test callback function: function(a,b) where a is the element to find and b the element tested
 * from the array.
 * @returns {boolean} true if at least one element is present in the array equals to the one to find according to the
 * compare function.
 * @author Vladimir de Turckheim
 */
Array.prototype.isPresent = function ( item , cpf ) {
  if ( ! cpf ) {
    cpf = function ( a , b ) {
      return a === b;
    }
  }
  return ! this.every ( function ( elt ) {
    return ! cpf ( item , elt );
  } );
};