Receive the previous value on change event

[aarongeorge]

It would be helpful to add a second parameter to the change callback so that you receive the previous value.

Is anyone opposed to this?

E.g.

const PARAMS = { index: 0 }

const pane = new Tweakpane()

pane.addInput(PARAMS, 'index', {
    step: 1,
    min: 0,
    max: 100
}).on('change', (newValue, previousValue) => {

    // If `index` was `0` and has been changed to `1`
    // `newValue` = 1
    // `previousValue` = 0
    console.log(newValue, previousValue)
})

[cocopon]

I think it would be useful in some situations but not suitable for general use. For example, previous values for MouseEvent (clientX, clientY, etc.) may also be useful but have not been implemented.

We also have to consider the second argument. (ref: #110) Maybe some kind of (ev: SomeTweakpaneEvent) => void would be better for this case.

[cocopon]

FYI, you can do it with one simple function like this:

const params = {
  foo: 50,
  bar: '#f00',
};

const pane = new Tweakpane();

// Create a handler that stores a previous value
function handlePrev(handler) {
  let prevValue = undefined;

  return (newValue) => {
    handler(newValue, prevValue);
    prevValue = newValue;
  };
}

pane.addInput(params, 'foo', {
  min: 0,
  max: 100,
  step: 1,
}).on(
  'change',
  handlePrev((newValue, prevValue) => {
    console.log(`[foo] new: ${newValue}, prev: ${prevValue}`);
  })
);

pane.addInput(params, 'bar').on(
  'change',
  handlePrev((newValue, prevValue) => {
    console.log(`[bar] new: ${newValue}, prev: ${prevValue}`);
  })
);

[LeonardoRick]

I think knowing the previous value of each bind would be really useful to implement a "undo" logic!