Edit in JSFiddle

function ValidateNumber(e, pnumber)
    {
        if (!/^\d+$/.test(pnumber))
        {
            var newValue =/^\d+/.exec(e.value);         
            if (newValue != null)         
            {             
                e.value = newValue;        
            }      
            else     
            {          
                e.value = "";    
            } 
        }
        return false;
    }

function ValidateFloat(e, pnumber)
{
    if (!/^\d+[.]?\d*$/.test(pnumber))
    {
        var newValue = /^\d+[.]?\d*/.exec(e.value);         
        if (newValue != null)         
        {             
            e.value = newValue;        
        }      
        else     
        {          
            e.value = "";    
        } 
    }
    return false;
}


function ValidateFloat2(e, pnumber)
{
    if (!/^\d+[.]?[1-9]?$/.test(pnumber))
    {
        var newValue = /\d+[.]?[1-9]?/.exec(e.value);         
        if (newValue != null)         
        {             
            e.value = newValue;        
        }      
        else     
        {          
            e.value = "";    
        } 
    }
    
    return false;
}

<p><input type="text" style="ime-mode:disabled" onkeyup="return ValidateNumber(this,value)" />只能輸入數字</p>

<p><input type="text" style="ime-mode:disabled" onkeyup="return ValidateFloat(this,value)" />可以輸入小數點</p>

<p><input type="text" style="ime-mode:disabled" onkeyup="return ValidateFloat2(this,value)" />可以輸入小數點（限制小數點後一位）</p>