Transforming traditional Javascript syntax into arrow function syntax

Question

Transforming traditional Javascript syntax into arrow function syntax

Seeking to utilize this example without relying on jquery or any other libraries.

The following code is in place:

let xmlHttp = new XMLHttpRequest();
xmlHttp.onreadystatechange = function() {...}

This code uses the old style function().

How can I convert this to arrow function syntax?

let xmlHttp = new XMLHttpRequest();
xmlHttp.onreadystatechange = () => {...}

I tried this but it did not work. Am I close, or am I approaching this incorrectly? Once again, I aim to complete this exercise without using external libraries.

javascript ajax xmlhttprequest arrow-functions

Answer 1

Answer №1

One issue with arrow functions is that they retain the this context of the enclosing scope.

In your initial example, the this reference would be bound to the XMLHttpRequest object rather than the window.

To address this in arrow notation, you can either refer to the XMLHttpRequest using an outer name like xmlHttp, or bind it to the callback function:

let xmlHttp = new XMLHttpRequest();
xmlHttp.onreadystatechange = ((request) => {...}).bind(undefined, request);

https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Global_Objects/Function/bind

It's important to note that arrow functions cannot have their this context overridden using methods such as bind, call, or apply.

Answer 2

One issue with arrow functions is that they retain the this context of the enclosing scope.

In your initial example, the this reference would be bound to the XMLHttpRequest object rather than the window.

To address this in arrow notation, you can either refer to the XMLHttpRequest using an outer name like xmlHttp, or bind it to the callback function:

let xmlHttp = new XMLHttpRequest();
xmlHttp.onreadystatechange = ((request) => {...}).bind(undefined, request);

https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Global_Objects/Function/bind

It's important to note that arrow functions cannot have their this context overridden using methods such as bind, call, or apply.

Answer 3

Answer №2

Bellian's code above is visually appealing, but the .bind(undefined, request); complicates it.

There is an alternative method that ensures synchronization with the expected answer to your questions:

I strongly suggest you follow this approach instead. By using an arrow function, you eliminate direct references to this, allowing for better accessibility to the results. Try running console.log(x) without the .target and see for yourself.

You can also:

let xmlHttp = new XMLHttpRequest();
xmlHttp.onreadystatechange = x => {
  let result = x.target;

        if(result.readyState == 4 && result.status == 200){         
            console.log(result.responseText);
            
        }
    
};

Answer 4

Bellian's code above is visually appealing, but the .bind(undefined, request); complicates it.

There is an alternative method that ensures synchronization with the expected answer to your questions:

I strongly suggest you follow this approach instead. By using an arrow function, you eliminate direct references to this, allowing for better accessibility to the results. Try running console.log(x) without the .target and see for yourself.

You can also:

let xmlHttp = new XMLHttpRequest();
xmlHttp.onreadystatechange = x => {
  let result = x.target;

        if(result.readyState == 4 && result.status == 200){         
            console.log(result.responseText);
            
        }
    
};

Transforming traditional Javascript syntax into arrow function syntax

Answer №1

Answer №2

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