Category: JavaScript Answers

Sometimes, we want to fix Failed to create chart: can’t acquire context from the given item with Chart.js and JavaScript.

In this article, we’ll look at how to fix Failed to create chart: can’t acquire context from the given item with Chart.js and JavaScript.

How to fix Failed to create chart: can’t acquire context from the given item with Chart.js and JavaScript?

To fix Failed to create chart: can’t acquire context from the given item with Chart.js and JavaScript, we should make sure the canvas is loaded before we create the chart.

For instance, we write

<canvas id="myChart" width="400" height="400"></canvas>

to add the canvas.

Then we write

const ctx = document.getElementById("myChart");
const ctx = document.getElementById("myChart").getContext("2d");
const ctx = document.querySelector("#myChart");
const ctx = "myChart";

const myChart = new Chart(ctx, {
  type: "line",
  data: {
    //...
  },
  options: {
    //...
  },
});

in a script tag below the canvas to run the code after the canvas is loaded to create the chart.

Conclusion

To fix Failed to create chart: can’t acquire context from the given item with Chart.js and JavaScript, we should make sure the canvas is loaded before we create the chart.

Sometimes, we want to delete default value of an input text on click with JavaScript.

In this article, we’ll look at how to delete default value of an input text on click with JavaScript.

How to delete default value of an input text on click with JavaScript?

To delete default value of an input text on click with JavaScript, we set the value property.

For instance, we write

<input
  type="text"
  value="[some default value]"
  onblur="onBlur(this)"
  onfocus="onFocus(this)"
/>

to add an input.

Then we write

function onBlur(el) {
  if (el.value === "") {
    el.value = el.defaultValue;
  }
}
function onFocus(el) {
  if (el.value === el.defaultValue) {
    el.value = "";
  }
}

to set the input’s value property to an empty string to empty the input box in the onFocus function when value is the same as defaultValue.

We set onfocus to onFocus(this) call it when we focus on it.

And we set onblur to onBlur(this) call it when we move focus away from it.

Conclusion

To delete default value of an input text on click with JavaScript, we set the value property.

Sometimes, we want to add a row on top of table generated by JavaScript.

In this article, we’ll look at how to add a row on top of table generated by JavaScript.

How to add a row on top of table generated by JavaScript?

To add a row on top of table generated by JavaScript, we call the insertRow method.

For instance, we write

const myTable = document.getElementById("myTable");
const tbody = myTable.tbodies[0];
const tr = tbody.insertRow(-1);

const td = document.createElement("td");
td.innerHTML = "Something";
tr.appendChild(td);

to select the table with getElementById.

Then we get the tbody element in it with myTable.tbodies[0].

Next, we call insertRow with -1 to insert the tr as the first child of the tbody element.

Then we create a td element with createElement and then call appendChild to append it as the last child of the tr.

We set its content by setting the innerHTML property.

Conclusion

To add a row on top of table generated by JavaScript, we call the insertRow method.

Sometimes, we want to check for any lowercase letters in a string with JavaScript.

In this article, we’ll look at how to check for any lowercase letters in a string with JavaScript.

How to check for any lowercase letters in a string with JavaScript?

To check for any lowercase letters in a string with JavaScript, we use a regex.

For instance, we write

const hasLowerCase = (str) => {
  return /[a-z]/.test(str);
};

to call /[a-z]/.test with str to check if str has any lower case letters.

Conclusion

To check for any lowercase letters in a string with JavaScript, we use a regex.

Sometimes, we wanty to add custom data formatting to display on tooltip with JavaScript Chart.js.

In this article, we’ll look at how to add custom data formatting to display on tooltip with JavaScript Chart.js.

How to add custom data formatting to display on tooltip with JavaScript Chart.js?

To add custom data formatting to display on tooltip with JavaScript Chart.js, we add a label callback.

For instance, we write

const chart = new Chart(ctx, {
  type: "line",
  data: data,
  options: {
    plugins: {
      tooltip: {
        callbacks: {
          label: (context) => {
            let label = context.dataset.label || "";

            if (label) {
              label += ": ";
            }
            if (context.parsed.y !== null) {
              label += new Intl.NumberFormat("en-US", {
                style: "currency",
                currency: "USD",
              }).format(context.parsed.y);
            }
            return label;
          },
        },
      },
    },
  },
});

to set the callbacks.label property to a function that returns the label contents.

context has the chart data.

Conclusion

To add custom data formatting to display on tooltip with JavaScript Chart.js, we add a label callback.