Validate input type numeric?

You can validate using Javascript that only accepts numerical values:

<input type="text" onkeypress='return event.charCode >= 48 && event.charCode <= 57'/>

I add a demo:

function validaNumericos(event) {
    if(event.charCode >= 48 && event.charCode <= 57){
      return true;
     }
     return false;        
}

<input type="text" onkeypress='return validaNumericos(event)'/>

We have the case in which a user can paste text and not just enter it, therefore we have to be prepared for that and not allow entering or pasting text that is not numeric:

function validaNumericos(){
 var inputtxt = document.getElementById('text'); 
 var valor = inputtxt.value;
 for(i=0;i<valor.length;i++){
     var code=valor.charCodeAt(i);
         if(code<=48 || code>=57){          
           inputtxt.value=""; 
           return;
         }    
   }
  
}

<input type="text" id="text" onblur="validaNumericos();" />

onload = function(){ 
  var ele = document.querySelectorAll('.validanumericos')[0];
  ele.onkeypress = function(e) {
     if(isNaN(this.value+String.fromCharCode(e.charCode)))
        return false;
  }
  ele.onpaste = function(e){
     e.preventDefault();
  }
}

   
<input class="validanumericos" type=text />

Another version but now using JQuery

$(function(){

  $('.validanumericos').keypress(function(e) {
	if(isNaN(this.value + String.fromCharCode(e.charCode))) 
     return false;
  })
  .on("cut copy paste",function(e){
	e.preventDefault();
  });

});

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<input class="validanumericos" type=text />

There is a response from @vinayakj with other options on the site in English. p>     

To validate the type of field is number and the minimum is negative.

<input type="number" min="0" step="1"/>

You need a regular expression to validate only numbers something like [0-9] , the following validates a 10 digit number but the last validation must be in server side language.

<input type="text" pattern="[0-9]{10}" />

If you want to use JavaScript then DO NOT USE JQUERY if your project is not using the library for anything else. Simple tasks are solved without loading a huge library for it.

Basically you need to add a function by pressing a key, by submitting a form or by clicking the submit:

<input type="text" onkeypress="validar_campo()">

<input type="submit" value="Login" onsubmit="return validar_campo()">

Now the function;

function validar_campo(evento){
 evento.value = evento.value.replace(/[^0-9]/g,"");
}

Something simpler on the same line ( @Max response ):

<input type="text" onkeypress="if ( isNaN( String.fromCharCode(event.keyCode) )) return false;" />