Use regular expression to remove bad words : Filter « Regular Expressions « JavaScript Tutorial

<html>
<head>
<title>Bad Words Example</title>
<script type="text/javascript">

        function filterText(sText) {
            var reBadWords = /badword|anotherbadword/gi;
            return sText.replace(reBadWords, function (sMatch) {
                return sMatch.replace(/./g, "*");
            });
        }

        function showText() {
            var oInput1 = document.getElementById("txt1");
            var oInput2 = document.getElementById("txt2");
            oInput2.value = filterText(oInput1.value);
        }
</script>
</head>
<body>
    <textarea rows="10" cols="50" id="txt1">badword anotherbadword</textarea><br />
    <input type="button" value="Filter Bad Words" onclick="showText()" /></p>
    <P>Filtered Text:<br />
    <textarea rows="10" cols="50" id="txt2"></textarea></p>

</body>
</html>

26.5.Filter
	26.5.1.	Trim the leading and trailing spaces
	26.5.2.	Strip HTML
	26.5.3.	Bad word filter
	26.5.4.	Use regular expression to remove bad words