How do you set the "Visible" property of a ASP.NET control from a Javascript function?

The "Visible" property of an ASP.NET control determines whether or not it will be rendered on the client (i.e. sent to the client). If it is false when the page is rendered, it will never arrive at the client.

So, you cannot, technically, set that property of the control.

That said, if the control is rendered on the client because the Visible property is true when the page is rendered, you can then hide it using javascript like this:

var theControl = document.getElementById("txtEditBox");
theControl.style.display = "none";

// to show it again:
theControl.style.display = "";

That assumes that the control's id attribute really is "txtEditBox" on the client and that it is already visible.

Also, is that the best way to hide/show a ASP.NET control from a Javascript function?

There is not necessarily a "best" way, although one better approach is to use CSS class definitions:

.invisible { display: none; }

When you want to hide something, dynamically apply that class to the element; when you want to show it again, remove it. Note, I believe this will only work for elements whose display value starts off as block.

instead of using visible, set its css to display:none

//css:
.invisible { display:none; }

//C#
txtEditBox.CssClass = 'invisible';
txtEditBox.CssClass = ''; // visible again

//javascript
document.getElementById('txtEditBox').className = 'invisible'
document.getElementById('txtEditBox').className = ''

Set the style to "display: none".

var theControl = document.getElementById("<%= txtEditBox.ClientID %>");
theControl.style.display = "none";