The synergy between Object.prototype and the bind() method

Question

The synergy between Object.prototype and the bind() method

Currently, I am delving into ngInfiniteScroll while being a novice in JavaScript. Upon reviewing the demo of ngInfiniteScroll, I find it quite challenging to comprehend why Reddit.nextPage has been altered to Reddit.prototype.nextPage, and how the bind() method is utilized to encapsulate a segment of the Reddit.prototype.nextPage function.

Below is the code snippet:

myApp.controller('DemoController', function($scope, Reddit) {
  $scope.reddit = new Reddit();
});

// Reddit constructor function for handling HTTP requests and pagination logic
myApp.factory('Reddit', function($http) {
  var Reddit = function() {
    this.items = [];
    this.busy = false;
    this.after = '';
  };

  Reddit.prototype.nextPage = function() {
    if (this.busy) return;
    this.busy = true;

    var url = "https://api.reddit.com/hot?after=" + this.after + "&jsonp=JSON_CALLBACK";
    $http.jsonp(url).success(function(data) {
      var items = data.data.children;
      for (var i = 0; i < items.length; i++) {
        this.items.push(items[i].data);
      }
      this.after = "t3_" + this.items[this.items.length - 1].id;
      this.busy = false;
    }.bind(this));
  };

  return Reddit;
});

I've recently grasped the concept that utilizing this allows access to properties within the Reddit object.

Could it be that because var Reddit is assigned an anonymous function, I need to bind the this from the anonymous function to the this in Reddit.nextPage so they refer to the same properties?

However, it appears feasible to access those properties even without using the bind() method. Consider the following example:

if (this.busy) return;
this.busy = true;

I have scoured through several articles on this topic but none provide an in-depth explanation, leaving me utterly confused.

javascript angularjs prototype bind factory

Answer 1

Answer №1

Exploring these functions:

Twitter.prototype.loadTweets = function() {
    // main function
    ...    
    $http.get(url).then(function(response) {
      // nested function
    }.bind(this));
  };

If we don't bind, the context of this in the inner function will be different, making it access different properties. However, using bind(this) instructs the inner function to refer to this from the main function's scope.

For further insights, I suggest reading this informative piece.

Answer 2

Exploring these functions:

Twitter.prototype.loadTweets = function() {
    // main function
    ...    
    $http.get(url).then(function(response) {
      // nested function
    }.bind(this));
  };

If we don't bind, the context of this in the inner function will be different, making it access different properties. However, using bind(this) instructs the inner function to refer to this from the main function's scope.

For further insights, I suggest reading this informative piece.

Answer 3

Answer №2

Although I haven't had the chance to explore the blog post yet, my assumption is that it was relocated to the prototype for the purpose of automatic inclusion in every instance of your "Reddit" service. Each time a new service is created, this method will be included because all prototype methods are inherited automatically.

As for the bind function, when passing a function as an argument, it loses its original context upon execution. This means it will no longer be bound to your Reddit service, instead taking on a new scope of execution. Consequently, references to this.items, this.busy, and this.after would all become undefined and lead to errors.

To delve deeper into this topic, you can learn more about bind(), call(), and apply().

Answer 4

Although I haven't had the chance to explore the blog post yet, my assumption is that it was relocated to the prototype for the purpose of automatic inclusion in every instance of your "Reddit" service. Each time a new service is created, this method will be included because all prototype methods are inherited automatically.

As for the bind function, when passing a function as an argument, it loses its original context upon execution. This means it will no longer be bound to your Reddit service, instead taking on a new scope of execution. Consequently, references to this.items, this.busy, and this.after would all become undefined and lead to errors.

To delve deeper into this topic, you can learn more about bind(), call(), and apply().

Answer 5

Answer №3

this can vary depending on the context. Here's an example:

var foo = {
  bar: function() {
    console.log(this.baz);
  },
  baz: 3
};

foo.bar(); // logs 3

However, in an asynchronous callback, the context changes. For instance, consider using setTimeout:

var foo = {
  bar: function() {
    setTimeout(function() { console.log(this.baz); }, 0);
  },
  baz: 3
};

foo.bar(); // logs undefined or throws an error in strict mode

In this case, 'this' no longer refers to foo. To work around this limitation, we can use bind:

var foo = {
  bar: function() {
    setTimeout((function() { console.log(this.baz); }).bind(this), 0);
  },
  baz: 3
};

foo.bar(); // logs 3

By binding the context to foo (the value of this at the call site), we are able to achieve the desired outcome. This is similar to how this is handled in the success handler of a promise returned by $http.jsonp.

Answer 6

this can vary depending on the context. Here's an example:

var foo = {
  bar: function() {
    console.log(this.baz);
  },
  baz: 3
};

foo.bar(); // logs 3

However, in an asynchronous callback, the context changes. For instance, consider using setTimeout:

var foo = {
  bar: function() {
    setTimeout(function() { console.log(this.baz); }, 0);
  },
  baz: 3
};

foo.bar(); // logs undefined or throws an error in strict mode

In this case, 'this' no longer refers to foo. To work around this limitation, we can use bind:

var foo = {
  bar: function() {
    setTimeout((function() { console.log(this.baz); }).bind(this), 0);
  },
  baz: 3
};

foo.bar(); // logs 3

By binding the context to foo (the value of this at the call site), we are able to achieve the desired outcome. This is similar to how this is handled in the success handler of a promise returned by $http.jsonp.

The synergy between Object.prototype and the bind() method

Answer №1

Answer №2

Answer №3

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