Limit text input to numbers (Javascript)

Limit the text field to only numbers (with decimals)

function format(input){
 var num = input.value.replace(/\,/g,'');
  if(!isNaN(num)){
   if(num.indexOf('.') > -1){
   num = num.split('.');
   num[0] = num[0].toString().split('').reverse().join('').replace(/(?=\d*\.?)(\d{3})/g,'$1,').split('').reverse().join('').replace(/^[\,]/,'');
   if(num[1].length > 2){
    alert('You may only enter two decimals!');
    num[1] = num[1].substring(0,num[1].length-1);
   } input.value = num[0]+'.'+num[1];
  } else {
   input.value = num.toString().split('').reverse().join('').replace(/(?=\d*\.?)(\d{3})/g,'$1,').split('').reverse().join('').replace(/^[\,]/,'') };
  } else {
   alert('You may enter only numbers in this field!');
   input.value = input.value.substring(0,input.value.length-1);
  }
}

Limit the text field to only numbers (no decimals)

function formatInt(input){
 var num = input.value.replace(/\,/g,'');
  if(!isNaN(num)){
   if(num.indexOf('.') > -1) {
    alert("You may not enter any decimals.");
    input.value = input.value.substring(0,input.value.length-1);
   }
  } else {
   alert('You may enter only numbers in this field!');
   input.value = input.value.substring(0,input.value.length-1);
  }
}

Call the function within the html input

<input id="text" name="text" size="5" onkeyup="format(this);">