IsNumeric in javascript

function IsNumeric(sText)
{
var ValidChars = "0123456789.";
var IsNumbe r= true;
var Char;
for (i = 0; i < sText.length && IsNumber == true; i++)
{
Char = sText.charAt(i);
if (ValidChars.indexOf(Char) == -1)
{
IsNumber = false;
}
if (Char =='.' && ValidChars.indexOf(Char)!= ValidChars.lastIndexOf(Char))
{
IsNumber=false;
}
}
return IsNumber;
}