Perform Numeric validation (Numbers) using OnKeyPress in JavaScript

Here Mudassar Ahmed Khan has explained with an example, how to perform Numeric validation i.e. allow only Numbers (Digits) using OnKeyPress event in JavaScript. When User types in the TextBox, the text in the TextBox will be validated using OnKeyPress event handler in JavaScript and if the inputted character is not Numeric i.e. Number (Digit), the error message will be displayed next to the TextBox.