Obtain the view property access while invoking render function as a callback

Question

Obtain the view property access while invoking render function as a callback

When working with the guid variable in the render() function, I encountered a limitation where I could only pass it to the constructor. Here is an example of the code I used:

app.views.CompanyView = Backbone.View.extend({
    el: '#company-view',
    guid: '',

    initialize: function (options) {
        this.guid = options.guid;
    },

    render: function () {
        var guid = this.guid;
    }
});

To instantiate my view, I followed this pattern:

app.currentView = new app.views.CompanyView({guid: guid});

Subsequently, I attempted to pass the render() function as a callback for usage:

function call(callback){
    callback();
}

call(app.currentView.render);

Various attempts such as using this.guid, options, and this.options resulted in the values being undefined. Is there a method to transmit this variable to the render() function without relying on its arguments or global variables? An illustrative example can be found in this JsFiddle link.

javascript backbone.js properties

Answer 1

Answer №1

When invoking render like this:

function execute(callback){
    callback();
}

The context of this within render will be the global window object, as you are calling it as a regular function. It is important to note that in JavaScript, the value of this is determined by how a function is called, not how it is defined (unless bound functions are used).

You have several options available:

Utilize _.bindAll, _.bind, $.proxy, Function.bind, to bind render to the view:
```
initialize: function() {
    _.bindAll(this, 'render');
}
```
Example: http://jsfiddle.net/ambiguous/GsUfY/
A more common practice nowadays is to supply a context when calling the callback and then utilize call or apply to specify the context:
```
function execute(callback, context){
    callback.apply(context);
}
```
Example: http://jsfiddle.net/ambiguous/LnwPr/
Manually manage the context:
```
execute(function() { v.render() });
```
This typically involves creating a variable like var _this = this; followed by an anonymous function that references _this.some_method() instead of directly passing this.some_method as a callback.

Example: http://jsfiddle.net/ambiguous/K2Xj4/

Personally, I favor the second approach.

Answer 2

When invoking render like this:

function execute(callback){
    callback();
}

The context of this within render will be the global window object, as you are calling it as a regular function. It is important to note that in JavaScript, the value of this is determined by how a function is called, not how it is defined (unless bound functions are used).

You have several options available:

Utilize _.bindAll, _.bind, $.proxy, Function.bind, to bind render to the view:
```
initialize: function() {
    _.bindAll(this, 'render');
}
```
Example: http://jsfiddle.net/ambiguous/GsUfY/
A more common practice nowadays is to supply a context when calling the callback and then utilize call or apply to specify the context:
```
function execute(callback, context){
    callback.apply(context);
}
```
Example: http://jsfiddle.net/ambiguous/LnwPr/
Manually manage the context:
```
execute(function() { v.render() });
```
This typically involves creating a variable like var _this = this; followed by an anonymous function that references _this.some_method() instead of directly passing this.some_method as a callback.

Example: http://jsfiddle.net/ambiguous/K2Xj4/

Personally, I favor the second approach.

Answer 3

Answer №2

It seems that when the render() function is triggered by the callback, the context of the method changes and "this" no longer refers to the view itself, but to the caller of the call function().

Take a look at this demo:

http://jsfiddle.net/xyz123/5/

var ContentView = Backbone.View.extend({
  initialize: function (options) {
      this.id = options.id;
  },

  render: function () {
    console.log('world');
    console.log(this);
  }
});

var content = new ContentView({id: '12345'});

function trigger(callback) {
  callback();
}

trigger(content.render);

When you check the console, you'll notice that "this" actually refers to the global window object.

To resolve this issue, you can bind the context to the view itself using _.bindAll();

initialize: function (options) {
    _.bindAll(this, "render");
    this.id = options.id;
}

Check out the updated demo on jsfiddle: http://jsfiddle.net/xyz123/6/

Answer 4

It seems that when the render() function is triggered by the callback, the context of the method changes and "this" no longer refers to the view itself, but to the caller of the call function().

Take a look at this demo:

http://jsfiddle.net/xyz123/5/

var ContentView = Backbone.View.extend({
  initialize: function (options) {
      this.id = options.id;
  },

  render: function () {
    console.log('world');
    console.log(this);
  }
});

var content = new ContentView({id: '12345'});

function trigger(callback) {
  callback();
}

trigger(content.render);

When you check the console, you'll notice that "this" actually refers to the global window object.

To resolve this issue, you can bind the context to the view itself using _.bindAll();

initialize: function (options) {
    _.bindAll(this, "render");
    this.id = options.id;
}

Check out the updated demo on jsfiddle: http://jsfiddle.net/xyz123/6/

Obtain the view property access while invoking render function as a callback

Answer №1

Answer №2

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