Allow only numeric input in textbox using jQuery

Allow only numeric input in textbox using jQuery

HTML

<form method="post" ENCTYPE = "multipart/form-data" onsubmit="return checkform(this);">
    <input type="text" class="decimal" id="number0" size="20" name="number[]">
    <input type="text" class="decimal" id="number1" size="20" name="number[]">
    <input type="text" class="decimal" id="number2" size="20" name="number[]">
    <input type="text" class="decimal" id="number3" size="20" name="number[]">
    <input type="text" class="decimal" id="number4" size="20" name="number[]">
    <input type="submit" name="submit" value="Next"/>
    </form>
    
    <script>
    function checkform ( form )
    {
        function getElementsByClassName(node, classname) {
            var a = [];
            var re = new RegExp('(^| )'+classname+'( |$)');
            var els = node.getElementsByTagName("*");
            for(var i=0,j=els.length; i<j; i++)
                if(re.test(els[i].className))a.push(els[i]);
            return a;
        }
        var list_decimal = getElementsByClassName(document.body,'decimal');
    
    
        for (z_decimal = 0; z_decimal < list_decimal.length; ++z_decimal) {
            var decimal_id_name = document.getElementsByClassName('decimal')[z_decimal].id
            alert(decimal_id_name);
        }
        return false ;
    }
    </script>