JavaScript validateion for blank space

function CheckSpace(c)
{


var val=c;
var str;
for(var i=0;i<=val.length-1;i++)
{
if(val.charAt(i)==' ')
{
str=true;
}
else
{
str=false;
break;
}
}
return str
}

//Method to call this function

var val = document.getElementById('<%=txtDescription.ClientID %>').value;
if(CheckSpace(val))
{
alert('Space is not allowed');
return false;
}