What are the recommended methods for binding a variable to an XMLHttpRequest object?

Question

What are the recommended methods for binding a variable to an XMLHttpRequest object?

const request = new XMLHttpRequest();
request.open('GET', 'example.php');
request.customVar = 0;
request.onreadystatechange = function(){
  this.customVar = this.responseText.length;
  const text = `${this.readyState}:${this.customVar}:${this.responseText}`;
  document.getElementById('x').innerHTML = text;
};

I have implemented this script in a webpage along with a <p id="x"></p>. I need to assign a custom variable for usage within the onreadystatechange function. It works well on the browsers I've tested so far, however, I am unsure if there is a standard naming convention that should be followed for custom variables.

Would it be advisable to prefix custom variables with an underscore or any other specific naming convention? Any guidance on this matter would be appreciated as using member variables feels more appropriate than resorting to global ones (especially since multiple XMLHttpRequest objects might be present on the page).

javascript ajax

Answer 1

Answer №1

If you want to master the art of efficient JavaScript programming, consider delving into the world of closures.

Let's say you have an ajax request tucked inside a function; in this scenario, you can define myVar using the var keyword and utilize it within the onreadystatechange function as though it were a local variable.

function x() {

    ....
    ....

    var xhr = new XMLHttpRequest();
    xhr.open('GET', 'example.php');
    var myVar = 0;
    xhr.onreadystatechange = function() {
        this.myVar = this.responseText.length;
        var s = this.readyState + ":" + myVar + ":" + this.responseText;
        document.getElementById('x').innerHTML = s;
    };

    ....
    ....

}

Answer 2

If you want to master the art of efficient JavaScript programming, consider delving into the world of closures.

Let's say you have an ajax request tucked inside a function; in this scenario, you can define myVar using the var keyword and utilize it within the onreadystatechange function as though it were a local variable.

function x() {

    ....
    ....

    var xhr = new XMLHttpRequest();
    xhr.open('GET', 'example.php');
    var myVar = 0;
    xhr.onreadystatechange = function() {
        this.myVar = this.responseText.length;
        var s = this.readyState + ":" + myVar + ":" + this.responseText;
        document.getElementById('x').innerHTML = s;
    };

    ....
    ....

}

Answer 3

Answer №2

It seems like you're on the right track with your current approach. You're not cluttering the overall scope and attaching to a known function. However, there are a few areas that could use some tweaking:

The variable name you've chosen is adequate for now, but what if you eventually need to use a variable named responseText?
Considering scoping might be beneficial.
Make sure to brush up on XHR implementations. At present, your code isn't compatible with IE7/8.

While many of these concerns may not arise with XHR due to its single callback nature, picture this scenario: you have a mysterious class called C with a callback function named feedback, which takes in closures. This callback triggers four times, each requiring the same variable to be passed without the possibility for it to be altered. Your current approach falls short in this instance. It may seem minor, but aiming for optimal solutions from the start is commendable. Plus, adhering to the DRY principle can be advantageous.

If I were to tackle this, my strategy would be as follows:

function callCObject(_c_init_vars, callback) {
  var tempObject = new C(); // Creating an instance of my "C" object
  var tCallback = function() {
     callback.apply(this,_c_init_vars);
  }
  tempObject.callback = tCallback;
  tempObject.run();
}

Rather than manually creating an instance of C, I'd opt for the following approach:

var myCallback = function(a,b,c) { console.log(a); console.log(b); };
callCObject([1,6], myCallback);

You can see the implementation in action here: http://jsfiddle.net/d3yAg/

Answer 4

It seems like you're on the right track with your current approach. You're not cluttering the overall scope and attaching to a known function. However, there are a few areas that could use some tweaking:

The variable name you've chosen is adequate for now, but what if you eventually need to use a variable named responseText?
Considering scoping might be beneficial.
Make sure to brush up on XHR implementations. At present, your code isn't compatible with IE7/8.

While many of these concerns may not arise with XHR due to its single callback nature, picture this scenario: you have a mysterious class called C with a callback function named feedback, which takes in closures. This callback triggers four times, each requiring the same variable to be passed without the possibility for it to be altered. Your current approach falls short in this instance. It may seem minor, but aiming for optimal solutions from the start is commendable. Plus, adhering to the DRY principle can be advantageous.

If I were to tackle this, my strategy would be as follows:

function callCObject(_c_init_vars, callback) {
  var tempObject = new C(); // Creating an instance of my "C" object
  var tCallback = function() {
     callback.apply(this,_c_init_vars);
  }
  tempObject.callback = tCallback;
  tempObject.run();
}

Rather than manually creating an instance of C, I'd opt for the following approach:

var myCallback = function(a,b,c) { console.log(a); console.log(b); };
callCObject([1,6], myCallback);

You can see the implementation in action here: http://jsfiddle.net/d3yAg/

What are the recommended methods for binding a variable to an XMLHttpRequest object?

Answer №1

Answer №2

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