Category: JavaScript Answers

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JavaScript Answers

How to Remove Whitespaces from the Start and End of a String with JavaScript?

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To remove whitespaces from the start and end of a string with JavaScript, we can use the replace method to find the line breaks from the start and end of the string.

Then we can replace them all with empty strings.

For instance, we can write:

const str = '    Hello   ';
const trim = str.replace(/^\s+|\s+$/g, '');
console.log(trim);

We have the str string with spaces at the start and end of the string.

Then we call replace with /^\s+|\s+$/ gto match all the whitespaces at the start and end of the string.

^ means start of the string and $ matches the end.

g matches all instances of the spaces.

The 2nd argument is an empty string so we replace all the matches with empty strings.

Therefore, trim is 'Hello’ .

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Chart.js JavaScript Answers

How to Handle Click Events on Charts in Chart.js?

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To handle click events on charts in Chart.js, we can add the onClick method into our chart.

Then we can use the getElementsAtEventForNode method to get the index of the data set entry that we clicked on.

For instance, we can write the following HTML:

<script src="https://cdn.jsdelivr.net/npm/chart.js"></script>
<canvas id="myChart" width="200" height="200"></canvas>

to add the script for Chart.js and canvas elements for the bar chart.

Then we can add the bar chart by writing:

const datasets = [{
  label: '# of Votes',
  data: [12, 19, 3, 5, 2, 3],
  backgroundColor: [
    'rgba(255, 99, 132, 0.2)',
    'rgba(54, 162, 235, 0.2)',
    'rgba(255, 206, 86, 0.2)',
    'rgba(75, 192, 192, 0.2)',
    'rgba(153, 102, 255, 0.2)',
    'rgba(255, 159, 64, 0.2)'
  ],
  borderColor: [
    'rgba(255,99,132,1)',
    'rgba(54, 162, 235, 1)',
    'rgba(255, 206, 86, 1)',
    'rgba(75, 192, 192, 1)',
    'rgba(153, 102, 255, 1)',
    'rgba(255, 159, 64, 1)'
  ],
  borderWidth: 1
}]

const ctx = document.getElementById("myChart").getContext('2d');
const myChart = new Chart(ctx, {
  type: 'bar',
  data: {
    labels: ["Red", "Blue", "Yellow", "Green", "Purple", "Orange"],
    datasets
  },
  options: {
    scales: {
      yAxes: [{
        ticks: {
          beginAtZero: true
        }
      }]
    },
    onClick(e) {
      const activePoints = myChart.getElementsAtEventForMode(e, 'nearest', {
        intersect: true
      }, false)
      const [{
        index
      }] = activePoints;
      console.log(datasets[0].data[index]);
    }
  }
});

We have the datasets array with the data, border color, and bar colors we want to display.

Also, we have the label to set the label of the legend.

Next, we have the options property set to an object with the onClick method to catch any clicks that were made on the chart.

In it, we call myChart.getElementsAtEventForNode method with the e event object, 'nearest' and an object with intersect set to true to get the nearest object that’s been clicked on.

It returns an array with the index of the dataset data entry that we clicked on.

Then we can get the value of the bar that we clicked on with:

datasets[0].data[index]
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JavaScript Answers

How to Clear a Drop Down List with jQuery?

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To clear a drop-down list with jQuery, we can use the empty or html method.

For instance, if we have the following dropdown and submit button:

<select>
  <option value='0' disabled selected>Select Value</option>
  <option value='1'>Value 1</option>
  <option value='2'>Value 2</option>
</select>

<input type="submit" value="click me" />

Then we can clear the dropdown with we click on the submit button with jQuery by writing:

$('input').on('click', () => {
  $('select').empty();
});

We add a click handler to the input element with on .

Then in the click handler, we call empty on the select dropdown to empty its entries.

We can do the same thing by calling html on the select dropdown with an empty string:

$('input').on('click', () => {
  $('select').html("");
});

The select dropdown will also be emptied once the button is clicked.

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JavaScript Answers

How to Set the HTML5 Audio Position with JavaScript?

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To set the position of an HTML5 audio clip with JavaScript, we can set the currentTime property of the audio element.

For instance, we can write the following HTML:

<audio src='https://file-examples-com.github.io/uploads/2017/11/file_example_MP3_700KB.mp3' controls>
</audio>

to add the audio element with the controls displayed with the controls attribute.

Then we get the audio element and set the currentTime in seconds by writing:

const audio = document.querySelector('audio')
audio.currentTime = 10;

We select the audio element with document.querySelector .

Then we set the currentTime to 10 to move the time to 10 seconds.

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JavaScript Answers

How to Determine Date Equality in JavaScript?

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To determine date equality with JavaScript, we can convert both dates to timestamps with the getTime method.

Then we can compare them directly since timestamps are integers.

For instance, we can write:

const d1 = new Date(2021, 1, 1)  
const d2 = new Date(2021, 1, 1)  
console.log(d1.getTime() === d2.getTime())

To create 2 dates d1 and d2 with the Date constructor.

We pass in the year, month, and day into the Date constructor to create the JavaScript date objects.

Then we call getTime on each to compare them directly as timestamps.

Therefore, the console log should log true since they are the same dates.