Why is variable in prototypal constructor undefined when accessed as a property?

Why is myPerson.age undefined?

function Person() {
  var age = 28;
}

var myPerson = new Person();

console.log(myPerson.age);

I have clearly set what the varaible is in the Person function construtor which 开发者_运维问答should be pointed to by the .prototype of myPerson, no?

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Try this:

function Person(){

    this.age = 28;

}


$(document).ready(function(){


  var myPerson = new Person();

  console.log(myPerson.age);


});