^{Note: This is an updated answer. Comments below refer to an old version which messed around with keycodes.}

jQuery

Try it yourself on JSFiddle.

There is no native jQuery implementation for this, but you can filter the input values of a text <input> with the following inputFilter plugin (supports Copy+Paste, Drag+Drop, keyboard shortcuts, context menu operations, non-typeable keys, the caret position, different keyboard layouts, validity error message, and all browsers since IE 9):

// Restricts input for the set of matched elements to the given inputFilter function.
(function($) {
  $.fn.inputFilter = function(callback, errMsg) {
    return this.on("input keydown keyup mousedown mouseup select contextmenu drop focusout", function(e) {
      if (callback(this.value)) {
        // Accepted value
        if (["keydown","mousedown","focusout"].indexOf(e.type) >= 0){
          $(this).removeClass("input-error");
          this.setCustomValidity("");
        }
        this.oldValue = this.value;
        this.oldSelectionStart = this.selectionStart;
        this.oldSelectionEnd = this.selectionEnd;
      } else if (this.hasOwnProperty("oldValue")) {
        // Rejected value - restore the previous one
        $(this).addClass("input-error");
        this.setCustomValidity(errMsg);
        this.reportValidity();
        this.value = this.oldValue;
        this.setSelectionRange(this.oldSelectionStart, this.oldSelectionEnd);
      } else {
        // Rejected value - nothing to restore
        this.value = "";
      }
    });
  };
}(jQuery));

You can now use the inputFilter plugin to install an input filter:

$(document).ready(function() {
  $("#myTextBox").inputFilter(function(value) {
    return /^\d*$/.test(value);    // Allow digits only, using a RegExp
  },"Only digits allowed");
});

Apply your preferred style to input-error class. Here's a suggestion:

.input-error{
  outline: 1px solid red;
}

See the JSFiddle demo for more input filter examples. Also note that you still must do server side validation!

Pure JavaScript (without jQuery)

jQuery isn't actually needed for this, you can do the same thing with pure JavaScript as well. See this answer.

HTML 5

HTML 5 has a native solution with <input type="number"> (see the specification), but note that browser support varies:

• Most browsers will only validate the input when submitting the form, and not when typing.
• Most mobile browsers don't support the step, min and max attributes.
• Chrome (version 71.0.3578.98) still allows the user to enter the characters e and E into the field. Also see this question.
• Firefox (version 64.0) and Edge (EdgeHTML version 17.17134) still allow the user to enter any text into the field.

Try it yourself on w3schools.com.

Here is the function I use:

// Numeric only control handler
jQuery.fn.ForceNumericOnly =
function()
{
    return this.each(function()
    {
        $(this).keydown(function(e)
        {
            var key = e.charCode || e.keyCode || 0;
            // allow backspace, tab, delete, enter, arrows, numbers and keypad numbers ONLY
            // home, end, period, and numpad decimal
            return (
                key == 8 || 
                key == 9 ||
                key == 13 ||
                key == 46 ||
                key == 110 ||
                key == 190 ||
                (key >= 35 && key <= 40) ||
                (key >= 48 && key <= 57) ||
                (key >= 96 && key <= 105));
        });
    });
};

You can then attach it to your control by doing:

$("#yourTextBoxName").ForceNumericOnly();

Inline:

<input name="number" onkeyup="if (/\D/g.test(this.value)) this.value = this.value.replace(/\D/g,'')">

Unobtrusive style (with jQuery):

$('input[name="number"]').keyup(function(e)
                                {
  if (/\D/g.test(this.value))
  {
    // Filter non-digits from input value.
    this.value = this.value.replace(/\D/g, '');
  }
});

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<input name="number">

You could just use a simple JavaScript regular expression to test for purely numeric characters:

/^[0-9]+$/.test(input);

This returns true if the input is numeric or false if not.

or for event keycode, simple use below :

     // Allow: backspace, delete, tab, escape, enter, ctrl+A and .
    if ($.inArray(e.keyCode, [46, 8, 9, 27, 13, 110, 190]) !== -1 ||
         // Allow: Ctrl+A
        (e.keyCode == 65 && e.ctrlKey === true) || 
         // Allow: home, end, left, right
        (e.keyCode >= 35 && e.keyCode <= 39)) {
             // let it happen, don't do anything
             return;
    }

    var charValue = String.fromCharCode(e.keyCode)
        , valid = /^[0-9]+$/.test(charValue);

    if (!valid) {
        e.preventDefault();
    }

You can use on input event like this:

$(document).on("input", ".numeric", function() {
    this.value = this.value.replace(/\D/g,'');
});

But, what's this code privilege?

• It works on mobile browsers(keydown and keyCode have problem).
• It works on AJAX generated content too, because We're using "on".
• Better performance than keydown, for example on paste event.

Short and sweet - even if this will never find much attention after 30+ answers ;)

  $('#number_only').bind('keyup paste', function(){
        this.value = this.value.replace(/[^0-9]/g, '');
  });

Use JavaScript function isNaN,

if (isNaN($('#inputid').val()))

if (isNaN(document.getElementById('inputid').val()))

if (isNaN(document.getElementById('inputid').value))

Update: And here a nice article talking about it but using jQuery: Restricting Input in HTML Textboxes to Numeric Values

$(document).ready(function() {
    $("#txtboxToFilter").keydown(function(event) {
        // Allow only backspace and delete
        if ( event.keyCode == 46 || event.keyCode == 8 ) {
            // let it happen, don't do anything
        }
        else {
            // Ensure that it is a number and stop the keypress
            if (event.keyCode < 48 || event.keyCode > 57 ) {
                event.preventDefault(); 
            }   
        }
    });
});

Source: http://snipt.net/GerryEng/jquery-making-textfield-only-accept-numeric-values

I use this in our internal common js file. I just add the class to any input that needs this behavior.

$(".numericOnly").keypress(function (e) {
    if (String.fromCharCode(e.keyCode).match(/[^0-9]/g)) return false;
});

Simpler one for me is

jQuery('.plan_eff').keyup(function () {     
  this.value = this.value.replace(/[^1-9\.]/g,'');
});

Why so complicated? You don't even need jQuery because there is a HTML5 pattern attribute:

<input type="text" pattern="[0-9]*">

The cool thing is that it brings up a numeric keyboard on mobile devices, which is way better than using jQuery.

You can do the same by using this very simple solution

$("input.numbers").keypress(function(event) {
  return /\d/.test(String.fromCharCode(event.keyCode));
});

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

I referred to this link for the solution. It works perfectly!!!

You can try the HTML5 number input:

<input type="number" value="0" min="0"> 

For non-compliant browsers there are Modernizr and Webforms2 fallbacks.

The pattern attribute in HTML5 specifies a regular expression that the element's value is checked against.

  <input  type="text" pattern="[0-9]{1,3}" value="" />

Note: The pattern attribute works with the following input types: text, search, url, tel, email, and password.

• [0-9] can be replaced with any regular expression condition.

• {1,3} it represents minimum of 1 and maximum of 3 digit can be entered.

Something fairly simple using jQuery.validate

$(document).ready(function() {
    $("#formID").validate({
        rules: {
            field_name: {
                numericOnly:true
            }
        }
    });
});

$.validator.addMethod('numericOnly', function (value) {
       return /^[0-9]+$/.test(value);
}, 'Please only enter numeric values (0-9)');

try it within html code it self like onkeypress and onpast

<input type="text" onkeypress="return event.charCode >= 48 && event.charCode <= 57" onpaste="return false">

function suppressNonNumericInput(event){
        if( !(event.keyCode == 8                                // backspace
            || event.keyCode == 46                              // delete
            || (event.keyCode >= 35 && event.keyCode <= 40)     // arrow keys/home/end
            || (event.keyCode >= 48 && event.keyCode <= 57)     // numbers on keyboard
            || (event.keyCode >= 96 && event.keyCode <= 105))   // number on keypad
            ) {
                event.preventDefault();     // Prevent character input
        }
    }

If have a smooth OneLiner:

<input type="text" onkeypress="return /[0-9]/i.test(event.key)" >

I came to a very good and simple solution that doesn't prevent the user from selecting text or copy pasting as other solutions do. jQuery style :)

$("input.inputPhone").keyup(function() {
    var jThis=$(this);
    var notNumber=new RegExp("[^0-9]","g");
    var val=jThis.val();

    //Math before replacing to prevent losing keyboard selection 
    if(val.match(notNumber))
    { jThis.val(val.replace(notNumber,"")); }
}).keyup(); //Trigger on page load to sanitize values set by server

You can use this JavaScript function:

function maskInput(e) {
    //check if we have "e" or "window.event" and use them as "event"
        //Firefox doesn't have window.event 
    var event = e || window.event 

    var key_code = event.keyCode;
    var oElement = e ? e.target : window.event.srcElement;
    if (!event.shiftKey && !event.ctrlKey && !event.altKey) {
        if ((key_code > 47 && key_code < 58) ||
            (key_code > 95 && key_code < 106)) {

            if (key_code > 95)
                 key_code -= (95-47);
            oElement.value = oElement.value;
        } else if(key_code == 8) {
            oElement.value = oElement.value;
        } else if(key_code != 9) {
            event.returnValue = false;
        }
    }
}

And you can bind it to your textbox like this:

$(document).ready(function() {
    $('#myTextbox').keydown(maskInput);
});

I use the above in production, and it works perfectly, and it is cross-browser. Furthermore, it does not depend on jQuery, so you can bind it to your textbox with inline JavaScript:

<input type="text" name="aNumberField" onkeydown="javascript:maskInput()"/>

I think it will help everyone

  $('input.valid-number').bind('keypress', function(e) { 
return ( e.which!=8 && e.which!=0 && (e.which<48 || e.which>57)) ? false : true ;
  })

Here is a quick solution I created some time ago. you can read more about it in my article:

http://ajax911.com/numbers-numeric-field-jquery/

$("#textfield").bind("keyup paste", function(){
    setTimeout(jQuery.proxy(function() {
        this.val(this.val().replace(/[^0-9]/g, ''));
    }, $(this)), 0);
});

This is why I recently wrote to accomplish this. I know this has already been answered but I'm leaving this for later uses.

This method only allows 0-9 both keyboard and numpad, backspaces, tab, left and right arrows (normal form operations)

$(".numbersonly-format").keydown(function (event) {
    // Prevent shift key since its not needed
    if (event.shiftKey == true) {
        event.preventDefault();
    }
    // Allow Only: keyboard 0-9, numpad 0-9, backspace, tab, left arrow, right arrow, delete
    if ((event.keyCode >= 48 && event.keyCode <= 57) || (event.keyCode >= 96 && event.keyCode <= 105) || event.keyCode == 8 || event.keyCode == 9 || event.keyCode == 37 || event.keyCode == 39 || event.keyCode == 46) {
        // Allow normal operation
    } else {
        // Prevent the rest
        event.preventDefault();
    }
});

I wrote mine based off of @user261922's post above, slightly modified so you can select all, tab and can handle multiple "number only" fields on the same page.

var prevKey = -1, prevControl = '';
$(document).ready(function () {
    $(".OnlyNumbers").keydown(function (event) {
        if (!(event.keyCode == 8                                // backspace
            || event.keyCode == 9                               // tab
            || event.keyCode == 17                              // ctrl
            || event.keyCode == 46                              // delete
            || (event.keyCode >= 35 && event.keyCode <= 40)     // arrow keys/home/end
            || (event.keyCode >= 48 && event.keyCode <= 57)     // numbers on keyboard
            || (event.keyCode >= 96 && event.keyCode <= 105)    // number on keypad
            || (event.keyCode == 65 && prevKey == 17 && prevControl == event.currentTarget.id))          // ctrl + a, on same control
        ) {
            event.preventDefault();     // Prevent character input
        }
        else {
            prevKey = event.keyCode;
            prevControl = event.currentTarget.id;
        }
    });
});

You would want to allow tab:

$("#txtboxToFilter").keydown(function(event) {
    // Allow only backspace and delete
    if ( event.keyCode == 46 || event.keyCode == 8 || event.keyCode == 9 ) {
        // let it happen, don't do anything
    }
    else {
        // Ensure that it is a number and stop the keypress
        if ((event.keyCode < 48 || event.keyCode > 57) && (event.keyCode < 96 || event.keyCode > 105 )) {
            event.preventDefault(); 
        }   
    }
});

Here is an answer that uses jQuery UI Widget factory. You can customize what characters are allowed easily.

$('input').numberOnly({
    valid: "0123456789+-.$,"
});

That would allow numbers, number signs and dollar amounts.

$.widget('themex.numberOnly', {
    options: {
        valid : "0123456789",
        allow : [46,8,9,27,13,35,39],
        ctrl : [65],
        alt : [],
        extra : []
    },
    _create: function() {
        var self = this;

        self.element.keypress(function(event){
            if(self._codeInArray(event,self.options.allow) || self._codeInArray(event,self.options.extra))
            {
                return;
            }
            if(event.ctrlKey && self._codeInArray(event,self.options.ctrl))
            {
                return;
            }
            if(event.altKey && self._codeInArray(event,self.options.alt))
            {
                return;
            }
            if(!event.shiftKey && !event.altKey && !event.ctrlKey)
            {
                if(self.options.valid.indexOf(String.fromCharCode(event.keyCode)) != -1)
                {
                    return;
                }
            }
            event.preventDefault(); 
        });
    },

    _codeInArray : function(event,codes) {
        for(code in codes)
        {
            if(event.keyCode == codes[code])
            {
                return true;
            }
        }
        return false;
    }
});

This seems unbreakable.

// Prevent NULL input and replace text.
$(document).on('change', 'input[type="number"]', function (event) {
    this.value = this.value.replace(/[^0-9\.]+/g, '');
    if (this.value < 1) this.value = 0;
});

// Block non-numeric chars.
$(document).on('keypress', 'input[type="number"]', function (event) {
    return (((event.which > 47) && (event.which < 58)) || (event.which == 13));
});

Here is two different approaches:

1. Allow numeric values with decimal point
2. Allow numeric values without decimal point

APPROACH 1:

$("#approach1").on("keypress keyup blur",function (e) {
   $(this).val($(this).val().replace(/[^0-9\.]/g,''));
      if ((e.which != 46 || $(this).val().indexOf('.') != -1) && (event.which < 48 || event.which > 57)) {
          event.preventDefault();
      }
});

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<h2>Numeric with decimal point</h2><br/>
<span>Enter Amount</span>
<input type="text" name="amount" id="approach1">

APPROACH 2:

$("#approach2").on("keypress keyup blur",function (event) {    
   $(this).val($(this).val().replace(/[^\d].+/, ""));
    if ((event.which < 48 || event.which > 57)) {
        event.preventDefault();
    }
});

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<h2>Numeric without decimal point</h2><br/>
<span>Enter Amount</span>
<input type="text" name="amount" id="approach2">

Need to make sure you have the numeric keypad and the tab key working too

 // Allow only backspace and delete
            if (event.keyCode == 46 || event.keyCode == 8  || event.keyCode == 9) {
                // let it happen, don't do anything
            }
            else {
                // Ensure that it is a number and stop the keypress
                if ((event.keyCode >= 48 && event.keyCode <= 57) || (event.keyCode >= 96 && event.keyCode <= 105)) {

                }
                else {
                    event.preventDefault();
                }
            }

I wanted to help a little, and I made my version, the onlyNumbers function...

function onlyNumbers(e){
    var keynum;
    var keychar;

    if(window.event){  //IE
        keynum = e.keyCode;
    }
    if(e.which){ //Netscape/Firefox/Opera
        keynum = e.which;
    }
    if((keynum == 8 || keynum == 9 || keynum == 46 || (keynum >= 35 && keynum <= 40) ||
       (event.keyCode >= 96 && event.keyCode <= 105)))return true;

    if(keynum == 110 || keynum == 190){
        var checkdot=document.getElementById('price').value;
        var i=0;
        for(i=0;i<checkdot.length;i++){
            if(checkdot[i]=='.')return false;
        }
        if(checkdot.length==0)document.getElementById('price').value='0';
        return true;
    }
    keychar = String.fromCharCode(keynum);

    return !isNaN(keychar);
}

Just add in input tag "...input ... id="price" onkeydown="return onlyNumbers(event)"..." and you are done ;)