Q197 How do I detect if text has been entered on a text input before the form has been submitted?

<script language="JavaScript"><!--
function validate() {
    if document.myForm.myText.value = '' {
        alert('Form field blank!');
        return false;
    }
    else
        return true;
}
//--></script>

<form name="myForm" onSubmit="return validate()">
<input type="text" name="myText">
<input type="submit">
</form>