Obtain additional information to address concerns related to onZoom and onPan issues on the line

Question

Obtain additional information to address concerns related to onZoom and onPan issues on the line

Attempting to enhance my Chart.js line chart by fetching more data or utilizing cached backup data during onZoom/onPan events has proven quite challenging.

The original code base is too intricate to share entirely, but I will outline the approaches I have taken so far.

1st approach: Using Chartjs-plugin-zoom for the onZoom and onPan callbacks. However, these callbacks do not provide any context (chart, x, y) during panning/zooming and are not functioning correctly. More details can be found here.

A pull request has been created to address some of these issues which is currently pending: Link

2nd approach: Attempting to modify data in the Chart.js chart using the beforeUpdate callback, but encountering various challenges. The graph initially displays around 1000 data points, updating every second. To handle zooming out, a backup data set containing additional data beyond the initial 1000 points is being considered. When zoomed out, the data set should expand based on changes in left and right coordinates detected in the beforeUpdate callback.

scales: {
    xAxes: [{
                    id: 'x-axis-0',
                    type: 'time',
                    beforeUpdate: function (chart) {
                        const scale = chart.chart.scales['x-axis-0']
                        if (scale.margins) {
                            const left = scale.getValueForPixel(scale.left)
                            const right = scale.getValueForPixel(scale.right)
                            const diffSec = (right - left) / 1000;
                            // Code snippet continued...
                        }
                    }
    }

The second method is resulting in errors such as:

TypeError: Cannot read property 'hidden' of undefined

Would appreciate insights into a potential 3rd solution.

EDIT: Experimentation with different versions has led to a semi-functional state where the first solution appears to be working. However, a new issue has arisen:

onZoom is triggered continuously while zooming instead of
```
Function called once zooming is completed
```
as indicated in the Readme, rendering it ineffective for fetching data from an API.

javascript vue.js chart.js chartjs-plugin-zoom

Answer 1

Answer №1

There is a lack of context in the onZoom and onPan callbacks of Chartjs-plugin-zoom, as mentioned in the documentation.

In fact, there is some context provided—it comes in the form of an object containing the chart. You can access it like so:

function handleCallback(context) {
  console.log('The chart is: ' + context.chart);
}

Answer 2

There is a lack of context in the onZoom and onPan callbacks of Chartjs-plugin-zoom, as mentioned in the documentation.

In fact, there is some context provided—it comes in the form of an object containing the chart. You can access it like so:

function handleCallback(context) {
  console.log('The chart is: ' + context.chart);
}

Answer 3

Answer №2

The solution I discovered is functioning perfectly within the beforeUpdate callBack.

In my graphs, I typically have 1-3 datasets, and this solution is effective regardless of the number of datasets you choose to include specifically for time series data only, utilizing allLabels and allData in the graph.

Although my use case is more complex, I am sharing a simple code snippet below for the beforeUpdate and filterData functions:


function filterData(chartInstance, leftLegendTime) {

    let diff = chartInstance.data.labels[0].getTime() - leftLegendTime
    // Ensure there's at least a 10-second difference between graph and zoomed out graph to avoid over-updating
    if (!chartInstance.data.labels || diff === 0 || diff <= 10000) return

    let allLabels = chartInstance.data.datasets[0].allLabels

    // Matching the start of the graph's left axis...
    let leftIndex = allLabels.map(
        (elem) => parseInt(elem.getTime()/1000)
    ).indexOf(parseInt(leftLegendTime/1000))

    if (leftIndex === -1) return;

    chartInstance.data = {...chartInstance.data, labels: allLabels.slice(leftIndex)}

    for (let i = 0; i < chartInstance.data.datasets.length; i++) {
        chartInstance.data.datasets[i] = {
            ...chartInstance.data.datasets[i],
            data: chartInstance.data.datasets[i].allData.slice(leftIndex)
        }
    }

    chartInstance.update()
}


// ...within graphOptions:
scales: {
        xAxes: [{
        id: 'x-axis-0',
        type: 'time',
        beforeUpdate: function (chart) {
        const scale = chart.chart.scales['x-axis-0']
        if (scale.margins) {
            const left = scale.getValueForPixel(scale.left)
            filterData(chart.chart, left._d.getTime())
        }
     }
}],
zoom: {
    enabled: true,
    drag: false, 
    mode: 'x',
    rangeMax: {
        x: new Date(Date.now() + 1000)
    },
    rangeMin: {
        x: new Date(Date.now() - 900 * 1000) // e.g., to display maximum history...
    }
}

Answer 4

The solution I discovered is functioning perfectly within the beforeUpdate callBack.

In my graphs, I typically have 1-3 datasets, and this solution is effective regardless of the number of datasets you choose to include specifically for time series data only, utilizing allLabels and allData in the graph.

Although my use case is more complex, I am sharing a simple code snippet below for the beforeUpdate and filterData functions:


function filterData(chartInstance, leftLegendTime) {

    let diff = chartInstance.data.labels[0].getTime() - leftLegendTime
    // Ensure there's at least a 10-second difference between graph and zoomed out graph to avoid over-updating
    if (!chartInstance.data.labels || diff === 0 || diff <= 10000) return

    let allLabels = chartInstance.data.datasets[0].allLabels

    // Matching the start of the graph's left axis...
    let leftIndex = allLabels.map(
        (elem) => parseInt(elem.getTime()/1000)
    ).indexOf(parseInt(leftLegendTime/1000))

    if (leftIndex === -1) return;

    chartInstance.data = {...chartInstance.data, labels: allLabels.slice(leftIndex)}

    for (let i = 0; i < chartInstance.data.datasets.length; i++) {
        chartInstance.data.datasets[i] = {
            ...chartInstance.data.datasets[i],
            data: chartInstance.data.datasets[i].allData.slice(leftIndex)
        }
    }

    chartInstance.update()
}


// ...within graphOptions:
scales: {
        xAxes: [{
        id: 'x-axis-0',
        type: 'time',
        beforeUpdate: function (chart) {
        const scale = chart.chart.scales['x-axis-0']
        if (scale.margins) {
            const left = scale.getValueForPixel(scale.left)
            filterData(chart.chart, left._d.getTime())
        }
     }
}],
zoom: {
    enabled: true,
    drag: false, 
    mode: 'x',
    rangeMax: {
        x: new Date(Date.now() + 1000)
    },
    rangeMin: {
        x: new Date(Date.now() - 900 * 1000) // e.g., to display maximum history...
    }
}

Obtain additional information to address concerns related to onZoom and onPan issues on the line

Answer №1

Answer №2

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