<input name="haha">
<input name="re" value="\d+">
<input name="button1" type="button" value="test" onclick="show(document.getElementById('re').value,document.getElementById('haha').value)">
<script language=javascript>
function show(validChar,inputValue){    
var regexStr="^"+validChar+"$"; 
var regex=new RegExp(regexStr); 
alert(regex.test(inputValue)); 
}
</script>

<input name="haha">
<input name="button1" type="button" value="test" onclick="show('\\d+',document.getElementById('haha').value)">
<script language=javascript>
function show(validChar,inputValue){    
var regexStr="^"+validChar+"$"; 
var regex=new RegExp(regexStr); 
alert(regex.test(inputValue)); 
}
</script>