Setting visibility of text field in JS

[hpl]

I want to set the visibility of a text field from a function in JS. I have tried this, but the code is not valid. What could be wrong?
[code]
function test() {
if (matval=="35") {
document.navform.text1.style.visibility = hidden;
} else {
document.navform.text1.style.visibility = visible;
}
}

[riis]

Put quotes around the property values: "visible" and "hidden".