javascript input via native popup

In the past, I've seen javascript alert() style popups but they had input fields in them.

These forms are much like the pr开发者_如何学Cimitive username/password field inputs you see when an .htpasswd file is used.

Can someone tell me how to implement this using regular javascript? (No libraries please)

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Yes, you're thinking of prompt. It's just:

var userInput = prompt("text to display", "default input text");

Note that this is just a general input mechanism. It's separate from the authentication dialog, though the underlying browser code may use the same GUI controls.