linq.js
function contains(item, equalityComparer) {
  equalityComparer = typeof equalityComparer === 'function' ? equalityComparer : util.defaultEqualityComparer;

  for (let i of this) {
    if (equalityComparer(i, item)) return true;
  }

  return false;
}
function contains(item, equalityComparer) {
  equalityComparer = typeof equalityComparer === 'function' ? equalityComparer : util.defaultEqualityComparer;

  for (let i of this) {
    if (equalityComparer(i, item)) return true;
  }

  return false;
}
function contains ( item , equalityComparer ) { equalityComparer = typeof equalityComparer === 'function' ? equalityComparer : util . defaultEqualityComparer ; for ( let i of this ) { if ( equalityComparer ( i , item ) ) return true ; } return false ; }
Determines whether a sequence contains a specified element by using the default equality comparer.

@param item The item which you want to check.
@param {(Function)} equalityComparer The equality comparer.
equalityComparer: (item1, item2) -> Boolean
Determines whether a sequence contains a specified element by using the default equality comparer .