What's the idea behind creating objects using Object.assign

Question

I'm reading through this Flux tutorial and the objects are created there like this:

var AppDispatcher = assign({}, Dispatcher.prototype, {

  /**
   * A bridge function between the views and the dispatcher, marking the action
   * as a view action.  Another variant here could be handleServerAction.
   * @param  {object} action The data coming from the view.
   */
  handleViewAction: function(action) {
    this.dispatch({
      source: 'VIEW_ACTION',
      action: action
    });
  }

});

They use Object.assign through polyfill. Since Object.assign copies all properties to the object as opposed to Object.create(prototype), I'm wondering what their motivation is to copy the properties directly onto AppDispatcher. Any ideas?

Josh Beam · Accepted Answer · 2015-09-17 04:29:52Z

1

It's just creating a copy of Dispatcher, based on its prototype.

If you were to do AppDispatcher = Dispatcher;, and then you mutate AppDispatcher, you would also be mutating Dispatcher. assign in this case just creates a safe copy, and then lets you assign properties to that copy.

answered Sep 17, 2015 at 4:29

Josh Beam

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7 Comments

Max Koretskyi Over a year ago

can you elaborate on that part ...based on its prototype? And how the same can be accomplished without using assign?

Josh Beam Over a year ago

@Maximus, You could do var AppDispatcher = Object.create(Dispatcher.prototype) and then set AppDispatcher.handleViewAction = /* whatever */. The way they do it is just for convenience. Makes it more concise. There's nothing fancy or hidden about it, it's just another way of doing it.

Max Koretskyi Over a year ago

with Object.create, properties available on Dispatcher.prototype will be accessible through prototype chain, but I thought that assign copies these properties and makes them own properties of AppDispatcher, no?

Josh Beam Over a year ago

@Maximus, if the polyfill assign directly mimicks Object.assign from ES6, then yes, assign will copy all of the prototype's properties directly onto the AppDispatcher. I haven't looked in the source of assign, but I assume that that's the case.

Max Koretskyi Over a year ago

So then Object.create approach is different, right?

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