Exploring an example of a Backbone application and implementing JavaScript techniques

I'm curious about the implementation in the Backbone example app () where the remaining() function is called using apply (this.without.apply(this, this.done());) instead of just this.without(this.done()).

 // Filter down the list of all todo items that are finished.
done: function() {
  return this.where({done: true});
},

// Filter down the list to only todo items that are still not finished.
remaining: function() {
  return this.without.apply(this, this.done());
},

Thank You !

#Update

Debugger output

this.without(this.done())
[child, child, child, child]
this.without.apply(this, this.done());
[child, child, child]

Answer №1

Utilizing a Dynamic List of Arguments

The essence lies in the specific way it is written:

function () {
  var args = slice.call(arguments);
  args.unshift(this.models);
  return _[method].apply(_, args);
}

This function expects a dynamically changing list of arguments, and one method to achieve this is by using apply:

...
return this.without.apply(this, ['pass', 'these', 'arguments']);

To delve deeper into the concept of apply, refer to the MDN documentation.

Answer №2

Do you wonder about the distinction between these two commands?

this.without( this.done() )

versus

this.without.apply( this, this.done() );

Let's simplify by eliminating the nested this.done() call. Now, the first one appears as:

var value = this.done();
this.without( value );

This snippet directly invokes this.without(), passing a single argument which is the result of calling this.done(). If that result happens to be an array, then the complete array is passed as a singular argument.

The second version transforms into:

var array = this.done();
this.without.apply( this, array );

In this instance, this.without() is invoked with a varying number of arguments, where each element from array becomes its own argument. (I've used

array<code> instead of <code>value
to emphasize that it must be an array for this code to function correctly.)

Moreover, when using .apply(), it not only passes the arguments but also sets the context of this within the called function, mirroring the behavior of a regular method call like this.without().

Answer №3

Utilizing apply enables you to define the specific "this" object for the function, which can be crucial in situations such as when it is invoked within a closure and the context of "this" may not align with your original intentions.

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