Question

I have a class that handles data. Other classes can give it their values and the data class will populate them.

It looks like this:

class Data

  constructor : ->
    @products = null

  populateProducts : (callback)=>
    ajaxCall (data)=>
      @products = data
      callback()

  allProducts : (list)=>
    if @products?
      list = @products
    else
      @populateProducts => allProducts list

The problem I am facing is that every method I add will have to check if products exists. So I am looking into ways to make that part of the code reusable.

One way I tried was the following:

  productsCheck : (callback)=>
    if @products?
      callback()
    else
      @populateProducts => products callback

Using this method I could simplify allProducts:

 allProducts : (list)=>
     @productsCheck => list = @products

In the end I am looking for technique that does: “if products don’t exists populate them from the database”. I was maybe thinking that this might be a known pattern so if that is the case information about it is also appreciated.

Answer 1

Because you’re loading @products asynchronously, and every method on the object has to (potentially) wait for @products to load, every method on the object is asynchronous and needs to return its result to a callback. There’s no way around this; you can’t make asynchronous JS code synchronous. allProducts can’t just return a value.

Here’s what you should do: First, change populateProducts so it won’t make an Ajax call if it doesn’t have to:

populateProducts : (callback) =>
  if @products?
    callback()
  else ajaxCall (data) =>
    @products = data
    callback()

Then just start each method that uses @products with a call to @populateProducts, like so:

allProducts : (callback) =>
  @populateProducts =>
    callback @products

firstProduct: (callback) =>
  @populateProducts =>
    callback @products[0]

# ...