lodash / underscore - set default parameters while ignoring unknown vars.

defaults.js

var Person = function(params) {
  this.name = "";
  this.age = 0;
  this.gender = "na";
    
  _.extend(this, _.pick(params, _.keys(this)));
};

var jason = new Person({
   name: "Jason",
   age: 29,
   gender: "M",
   occupation: "programmer"
});

console.log(jason);

// produces: {name: "Jason", age: 29, gender: "M"}