<input value="" type="text" onkeyup="javascript:RepNumber(this)">

function RepNumber(obj) {
  var reg = /^[\d]+$/g;
  if (!reg.test(obj.value)) {
    var txt = obj.value;
    txt.replace(/[^0-9]+/,
    function(char, index, val) { //匹配第一次非数字字符
      obj.value = val.replace(/\D/g, ""); //将非数字字符替换成""
      var rtextRange = null;
      if (obj.setSelectionRange) {
        obj.setSelectionRange(index, index);
      } else { //支持ie
        rtextRange = obj.createTextRange();
        rtextRange.moveStart('character', index);
        rtextRange.collapse(true);
        rtextRange.select();
      }
    })
  }
}

function chkNumber(eleText)
    {
       var value =eleText.value;
       var len =value.length;
       for(vari=0;i<len;i++)
       {
           if(value.charAt(i)>"9"|| value.charAt(i)<"0")
           {
              alert("含有非数字字符");
              eleText.focus();
              break;
           }
       }
    }