Using Javascript to connect with server using protocol other than HTTP

Can Javascript be used to connect with a server 开发者_JAVA技巧with a protocol other than HTTP or FILE? Ideally, I would like to connect to an SMTP server using Javascript.

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Not possible due to security constraints in the browser. Can be done in flash or java as far as I know. The upcoming WebSockets won't help you either.

Your best option is probably to call a script on your server which makes the socket connections to the final destination, i.e the SMTP server and then passes data back to the client over HTTP.

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You do not have socket access with browser-integrated JavaScript, it would violate the sandbox security model. So no, no SMTP, or any other protocol. Even file:// should be rather difficult.

Server based JavaScript like node.js can do things like this.

Accessing e.g. SMTP via the browser is usually done through a proxy script that runs on the server and speaks HTTP to the client.