to convert alpha numeric string to a lower case in javascript
<p>I am reading a text field, and converting that value to Lower case and 
comparing to the array of words, if it matches it throws error.</p>

<p>But the problem is when we enter a text as a Alpha Numeric value, then I am not able to convert Lower case letters
and getting the Run Time error as "Object is Not Defined"</p>

<pre><code>if(streetAddress != null){
    for(var k=0; k&lt;notValidPostalChars.length; k++){

        var secondWord = notValidPostalChars[k];

        if (streetAddress.toLowerCase().startsWith(stopWord.toLowerCase())) {
            alert("Invalid Error Message");
            document.getElementById("address").focus();
        return false;
        }

    }
}
</code></pre>

<p>In the above Example, streetAddress may contain the Alpha Numeric as well and it might be in the Lower case or Upper case letters.</p>

<p>This will be entered by the End users and notValidPostalChars is an Array consisting of all the Pre defined Words with UPPER CASE letters</p>
