The impact of a variable in a function with XMLHttpRequest

Question

The impact of a variable in a function with XMLHttpRequest

How does the XMLHttpReqeust variable impact the functionality of the following code snippets?

function getHTTPObject() {
    if (typeof XMLHttpRequest == "undefined") {
        XMLHttpRequest = function () {
            try {
                return new ActiveXObject('Msxml2.XMLHTTP.6.0');
            } catch (e) {

            }
            try {
                return new ActiveXObject('Msxml2.XMLHTTP.3.0');
            } catch (e) {

            }
            try {
                return new ActiveXObject('Msxml2.XMLHTTP');
            } catch (e) {

            }
            return false;
        }
     }
     return new XMLHttpRequest();
}

I conducted an experiment by removing the XMLHttpRequest variable and found that the code continued to work as expected. Does it simply create an anonymous function in this case?

javascript ajax

Answer 1

Answer №1

Purpose of the function:

The main objective of this function is to check if the symbol XMLHttpRequest is defined in the browser. This is used to determine if the browser supports Ajax calls natively or not.

Furthermore, I recommend removing this code unless there is a specific requirement to support IE6, as it is no longer necessary.

For example:

var x = 3;

console.log(typeof x);    // "number"
console.log(typeof y);    // "undefined"

// And, in any modern browser
console.log(typeof XMLHttpRequest);  // "function"

// In IE6
console.log(typeof XMLHttpRequest);  // "undefined"

This type of check for the presence of the XMLHttpRequest object is specifically for very old Microsoft browsers (IE6 and older) and is now considered obsolete and can be safely removed.

Actual behavior of the function:

This function essentially creates a new instance of XMLHttpRequest() every time it is called.

Since your if condition

if (typeof XMLHttpRequest == "undefined")

will always result in false, the line return new XMLHttpRequest(); will be executed each time the function is called.

Therefore, a new XMLHttpRequest instance is created on every execution.

Understanding XMLHttpRequest:

The XMLHttpRequest object facilitates data exchange with a server behind the scenes. It enables updating a web page without reloading it, requesting data from a server after the page has loaded, and receiving data from a server after the page has loaded.

In essence, it is utilized for making AJAX calls to the server. For comprehensive information about XMLHttpRequest, you can refer to this resource.

I trust that this explanation clarifies your query.

Answer 2

Purpose of the function:

The main objective of this function is to check if the symbol XMLHttpRequest is defined in the browser. This is used to determine if the browser supports Ajax calls natively or not.

Furthermore, I recommend removing this code unless there is a specific requirement to support IE6, as it is no longer necessary.

For example:

var x = 3;

console.log(typeof x);    // "number"
console.log(typeof y);    // "undefined"

// And, in any modern browser
console.log(typeof XMLHttpRequest);  // "function"

// In IE6
console.log(typeof XMLHttpRequest);  // "undefined"

This type of check for the presence of the XMLHttpRequest object is specifically for very old Microsoft browsers (IE6 and older) and is now considered obsolete and can be safely removed.

Actual behavior of the function:

This function essentially creates a new instance of XMLHttpRequest() every time it is called.

Since your if condition

if (typeof XMLHttpRequest == "undefined")

will always result in false, the line return new XMLHttpRequest(); will be executed each time the function is called.

Therefore, a new XMLHttpRequest instance is created on every execution.

Understanding XMLHttpRequest:

The XMLHttpRequest object facilitates data exchange with a server behind the scenes. It enables updating a web page without reloading it, requesting data from a server after the page has loaded, and receiving data from a server after the page has loaded.

In essence, it is utilized for making AJAX calls to the server. For comprehensive information about XMLHttpRequest, you can refer to this resource.

I trust that this explanation clarifies your query.

Answer 3

Answer №2

This script serves as a polyfill to provide XMLHttpRequest functionality for outdated versions of Internet Explorer. Prior versions of IE rely on a proprietary ActiveX interface rather than the traditional XMLHttpRequest API.

For Internet Explorer 7 and newer versions, the standard XMLHttpRequest object is already supported. This code can be omitted unless you are specifically catering to users on IE 6 or earlier.

Answer 4

This script serves as a polyfill to provide XMLHttpRequest functionality for outdated versions of Internet Explorer. Prior versions of IE rely on a proprietary ActiveX interface rather than the traditional XMLHttpRequest API.

For Internet Explorer 7 and newer versions, the standard XMLHttpRequest object is already supported. This code can be omitted unless you are specifically catering to users on IE 6 or earlier.

The impact of a variable in a function with XMLHttpRequest

Answer №1

Answer №2

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