DOM Access Control Using Cross-Origin Resource Sharing.
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AJAX calls can be deceptive in the sense that cached information may be used when available. This is a disaster for real-time data fetches. The server can control browser caching of its pages by setting the Cache-control header to no-cache and the Expires header to a past date.
The request header fields allow the client to pass metadata about the request, and about the client itself, to the server. These fields act as request modifiers, with semantics equivalent to the parameters on a programming language method invocation. It is important to recognize that this data is accepted raw from the client without any kind of validation.
The HTTP request carries this language preference information in the Accept-Language header. If the server is set up to return alternate versions of a page or resource in more than one language, and the language you prefer is available, it will go through a process known as HTTP content negotiation to find content in the language(s) indicated in the HTTP request.
Creating the XMLHttpRequest object This example application is going to need an XMLHttpRequest object to start, so it begins with the code that will create that object; this code is outside any function, so it runs immediately as the page loads. You start everything by creating a variable for this object, XMLHttpRequestObject like this: 83 84 Part II: Programming in Ajax In this function, the.
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A famous example of this is Gmail (or Google Inbox), where archiving an email will happen immediately on the UI while the server request is sent and processed asynchronously. In the case of a form, instead of waiting for some HTML as a response after its submission, we can act right after the user presses enter.