Get getMinMax from a scale

[ronildo]

I'm trying to get the min-max values from a scale, but the method I found to use it's a protected method.

Is there another way to get these values without using a protected method?

This is the code I'm using:

const visibleMetas = chart.getSortedVisibleDatasetMetas()

const minMaxScale = visibleMetas.map(meta => ({
  ...meta.controller.getMinMax(chart.scales.y, true)
}))

A bit more context:
I'm using this function to keep all data visible in the chart as the user pan/zoom on it. I couldn't find any option to do that without getting the mix/max for the scale.

[ronildo]

@stockiNail any idea on how I can achieve this? thanks 🙏

[stockiNail]

@ronildo I will have a look tomorrow. I think there is a method on the scale to get min and max. And you could use meta vScale or yScale to get the scale for values. More tomorrow.

[ronildo]

Thank you for taking your time to help me! I really appreciate it.
I think I tried to use the yScale, but it wouldn't give the min-max from the visible area, it would give me from the whole chart.

[stockiNail]

@ronildo as far as I understood, you are trying to access to the controller to get min and max. Let me assume you are using the line controller (but it could be the same for bar or others).

To be compliant with Chart.js code and visibility of the methods, you could extend the existing line controller adding a public method which is invoking the getMinMax one.

Here I'm creating my LINE controller (vanillaJS but it's the same with other framework but you need to import the controller and remove Chart namespace).

// Controller
class MyLineController extends Chart.LineController {
  
  getMaxMin(scale, canStack) {
    return super.getMinMax(scale, canStack);
  }
  
};
MyLineController.id = 'myLine';
MyLineController.defaults = Chart.LineController.defaults;
Chart.register(MyLineController);

Note that I have changed the name of the method in getMaxMin instead of getMinMax.

In your chart you can set the chart type to 'myLine' as following:

// Chart
const config = {
  type: 'myline',
  data: {
  ......

Then you code could be:

      const visibleMetas = chart.getSortedVisibleDatasetMetas();
      const minMaxScale = visibleMetas.map(meta => ({
        ...meta.controller.getMaxMin(chart.scales.y, true) // <--- new method of your controller
      }));

See codepen: https://codepen.io/stockinail/pen/PoyOqNY
Clicking on the chart, I'm invoking your logic and log the result.

You could do the same at scale level (creating your scale extension) but I think it could be more complex, if I have understood well your use case.
Let me know if make sense to you and if is working for you.

[kurkle]

Depending on when the values are needed, scale.min and scale.max are public properties available after the scale is updated.

[stockiNail]

@kurkle for my curiosity, is there a reason why getMinMax is protected?

[kurkle]

If my memory serves, just so it can be changed without breaking changes / does not need to be compatible between versions / can be removed. It was created for internal need.

[stockiNail]

No sure if it's not a breaking change because whoever is implementing own scales of controllers could use that method therefore if changed, it breaks the implementation.

[ronildo]

@stockiNail I believe your solution might work for my project, but as you said in your last comment, it still would break if that method is updated. At least it would hide the error for me.

In the next few days, I will try to add an example of why I use this function, you might know an easier for me to accomplish the same thing without needing the min-max function.
For now, thank you so much 🙏

@kurkle if this method could be exposed as a public method it would be perfect.