Allow only numbers to be typed in a textbox [duplicate]

Question

How to allow only numbers to be written in this textbox ?

<input type="text" class="textfield" value="" id="extra7" name="extra7">

Answer 1

With HTML5 you can do

<input type="number">

You can also use a regex pattern to limit the input text.

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

Answer 2

You also can use some HTML5 attributes, some browsers might already take advantage of them (type="number" min="0").

Whatever you do, remember to re-check your inputs on the server side: you can never assume the client-side validation has been performed.