Sure! Here's an example of a simple calculator app implemented as a single HTML file using JavaScript:
Calculator
This calculator app allows you to perform basic arithmetic operations such as addition, subtraction, multiplication, and division. The result is displayed in the input field, and you can input numbers and operators by clicking on the corresponding buttons.
Please note that this is just a basic example, and there are more advanced calculators and validation techniques that you can implement based on your specific requirements.