I have some inputs defined in react. I'm assigning a function to their `onChange` function. I can find the current value. How can I get the old value in simplest way?

The reason I want this is because I want to find the ratio of this new value to the old value and do some operations.

Sample code:

```
let onChange = (e) => {
    let newValue = e.target.value; // let oldValue = will be here     

}

<Input type="number"  onChange={onChange }></Input>

```