function to validate text box on blank or default text

function checkForm(f) {
    if (f.elements['zoom_query'].value == "" || "Search - Movie or Actor") {
        f.zoom_query.focus();
        return false;
    } else {
        f.submit();开发者_运维百科
        return false;
    }
}

this prevents form submission for any string

any idea?

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I think it should read:

(f.elements['zoom_query'].value == "" || f.elements['zoom_query'].value == "Search - Movie or Actor")

Otherwise it always evaluates true

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If you can use jQuery I'd recommend having a look here: http://docs.jquery.com/Plugins/validation

And this question contains an answer that solves the problem you're having using jQuery Form Validation.

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function checkForm(f) {

    if (f.zoom_query.value == "" || f.zoom_query.value == "Search - Movie or Actor") {
        alert("Please fill in the text field.");
        f.zoom_query.focus();
        return (false);
    }

    f.submit();
    return (true);
}