Utility function for checking if something exists.

gistfile1.js

// Check existence
function exists(thing) {
  return (!isNaN(thing) && typeof thing !== 'undefined' && thing !== null) ? thing : undefined;
}

// Or, more tersely
function exists(thing) {
  // != checks `null` and `undefined`
  return thing != null ? thing : undefined;
}

/*
  Usage...

  var options = {
    latitude: 0,
    longitude: 1
  };

  var lat = exists(options.latitude);
  var lon = exists(options.longitude);
*/

After being bitten by loose existence checking…

var foo = o.bar || undefined;

And having it bomb out on values that are 0 (falsey), I've started using this little exists function to handle variable assignment where a valid value can be zero.

thing != null simply will check both the null and undefined cases, but no other cases. I think preferable to checking both cases explicitly like this.

@getify Good call. Forgot about that.