Underscore.js isDefined mixin

_.isDefined.js

// Underscore.js isDefined mixin
// Returns true if value is defined.
_.mixin({
    isDefined: function(reference) {
        return !_.isUndefined(reference);
    }
});

/* Example:
    var obj = {
        definedProperty: 10
    };

    _.isDefined(obj.definedProperty);
    => true

    _.isDefined(obj.aBunchOfCrazyMonkeysProperty);
    => false
*/

I wrote this function because I personally hate the if(!_.isUndefined(....)) {} expression. I believe that isDefined() is more clear for a reader. Have no idea why it's missing in Underscore framework itself. Inspired by angular.isDefined