XHR responseText is empty string

Question

Html Page:

    
    

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Answer 1

The call to send is asynchronous (you've set the 'async' parameter to true), which means that your alert is happening immediately, before the request finishes. You should add an event-listener to xhr.onreadystatechange and use the response within that.

Changing the 'true' to 'false' would make this simple example work, but is not a good idea in the general case.

The MDN page on Ajax explains how XMLHttpRequest should be used.