Is there any issue with this brief declaration of XMLHttpRequest?

After exploring various AJAX libraries, I have noticed that XMLHttpRequest typically involves a lengthy declaration with testing or try/catch statements.

I am trying to fetch XML through a SOAP GET request and found success in testing the following declaration across IE7+, Firefox, and Chrome:

var xhr=new XMLHttpRequest()||new ActiveXObject("Microsoft.XMLHTTP");

Is there something crucial that I may be overlooking? Are there any edge cases that could potentially cause my declaration to fail?

Edit

It appears that the second part of the declaration is never executed. Does this mean that for IE7+/Firefox/Chrome, all I really need is:

var xhr=new XMLHttpRequest();
javascriptajaxxmlhttprequestactivexobject

Answer №1

If you're worried about compatibility with Internet Explorer versions older than 7, consider the following:

new ActiveXObject("MSXML2.XMLHTTP");

Instead of directly calling this method, it might be more efficient to create a generic function like createRequest() that automatically selects the appropriate object based on the browser being used. This approach can also include error handling using try/catch blocks for better reliability.

Answer №2

The precedence of new is important here, meaning that new XMLHttpRequest() will be executed first and the return value checked. However, if XMLHttpRequest is not defined, an error will already occur during this execution. To avoid this, it's better to check if XMLHttpRequest is defined before using new, like so:

var xhr = typeof XMLHttpRequest === "undefined"
            ? new ActiveXObject("Microsoft.XMLHTTP")
            : new XMLHttpRequest; // you can omit the parentheses when there are no arguments

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