CODEWITHSUNDEEP
javascriptobjectprototype
amarshall
amarshall

Reputation: 63

Expose prototypes in object

Is there a way to expose an objects' prototypes through another object?

  var foo = function () {
    var foo = {
      bar: bar,
      boo: boo
    }
    return foo;

    function bar (age) {
      this.age = age;
    }
    bar.prototype.shoutAge = function () {
      alert('My age is ' + this.age);
    }

    function boo (age) {
      this.age = age;
      boo.prototype.shoutAge = function () {
        alert('My age is ' + this.age);
      }
    }
  }

  var foo = foo();
  var far = new foo.bar(13); // bar {age: 13}
  far.shoutAge(); // far.shoutAge is not a function

  var far = new foo.boo(13); // boo {age: 13} with __proto__
  far.shoutAge(); // alert('My age is 13');

In this code, the 'bar' object is set up with prototype inheritance--but exposing bar loses the inheritance of 'shoutAge'.

However, the 'boo' object has the prototype declared inside of it and the outside function has access to the method 'shoutAge'.

I don't think that the latter is a best practice even though it functions. So what would the best practice here be?

I don't want each instance of 'bar' to have it's own 'shoutAge' method, especially if there are potentially hundreds of instances of 'bar'. Would you typically just create a separate object for 'bar' instead of exposing it through 'foo'?

Upvotes: 6

Views: 163

Answers (1)

nrabinowitz
nrabinowitz

Reputation: 55678

Looks like this is just an order-of-operations issue:

var Foo = function () {

  function bar (age) {
    this.age = age;
  }
  bar.prototype.shoutAge = function () {
    alert('My age is ' + this.age);
  }

  var foo = {
    bar: bar,
    boo: boo
  }
  return foo;
}

I think this is because the bar.prototype assignment is never executed in your code. The bar function definition gets hoisted, so it's available in the object you return, but the prototype assignment is an additional statement after the return statement, and the control flow never reaches it. Simply moving the return to the end fixes the issue.

Upvotes: 3

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