Category: JavaScript Answers

Sometimes, we want to get the index of an element in JavaScript.

In this article, we’ll look at how to get the index of an element in JavaScript.

How to get the index of an element in JavaScript?

To get the index of an element in JavaScript, we can use the spread operator to spread a node list into an array.

Then we can use the array’s indexOf method to get the index.

For instance, we write:

const nodes = document.getElementsByTagName('*');
const nodesArr = [...nodes]
const index = nodesArr.indexOf(document.body)
console.log(index)

to select all elements with getElementsByTagName.

Then we spread the nodes into an array and assign it to nodesArr.

Next, we call nodesArr.indexOf with the element we’re trying to find the index for.

Then we get that the index is 0 or greater if the element we’re searching for is in the array.

Conclusion

To get the index of an element in JavaScript, we can use the spread operator to spread a node list into an array.

Then we can use the array’s indexOf method to get the index.

Sometimes, we want to check if an input value is empty and display an alert with JavaScript.

In this article, we’ll look at how to check if an input value is empty and display an alert with JavaScript.

How to check if an input value is empty and display an alert with JavaScript?

To check if an input value is empty and display an alert with JavaScript, we can check the value property of the input to see if it’s blank.

For instance, we write:

<form>
  <input>
  <button type='submit'>submit</button>
</form>

to add a form.

Then we write:

const form = document.querySelector('form')
const input = document.querySelector('input')

form.onsubmit = (e) => {
  e.preventDefault()
  if (!input.value) {
    alert('Input can not be left blank');
  }
}

to select the form and the input with querySelector.

Then we set the form.onsubmit to a function that checks if the input value is blank with !input.value.

If it’s true, then we display the alert.

Conclusion

To check if an input value is empty and display an alert with JavaScript, we can check the value property of the input to see if it’s blank.

Sometimes, we want to make a HTML5 video loop seamlessly with JavaScript.

In this article, we’ll look at how to make a HTML5 video loop seamlessly with JavaScript.

How to make a HTML5 video loop seamlessly with JavaScript?

To make a HTML5 video loop seamlessly with JavaScript, we can watch when the video almost ends and then set its time back to the start time.

For instance, we write:

<video width="300" height="300" controls loop autoplay preload="true">
  <source src="https://file-examples-com.github.io/uploads/2017/04/file_example_MP4_480_1_5MG.mp4" type="video/mp4">
</video>

to add a video element.

Then we write:

const vid = document.querySelector("video");
vid.addEventListener("timeupdate", (e) => {
  if (e.target.currentTime >= 29) {
    e.target.currentTime = 0.0;
  }
});

We select the video with querySelector.

Then we call addEventListener with 'timeupdate' to listen for the timeupdate event.

If the currentTime of the video is close to the end, then we set the currentTime back to 0 to restart the video.

Conclusion

To make a HTML5 video loop seamlessly with JavaScript, we can watch when the video almost ends and then set its time back to the start time.

Sometimes, we want to sum all the digits of a number JavaScript.

In this article, we’ll look at how to sum all the digits of a number JavaScript.

How to sum all the digits of a number JavaScript?

To sum all the digits of a number JavaScript, we can use some array methods.

For instance, we write:

const value = 2568;
const sum = value
  .toString()
  .split('')
  .map(Number)
  .reduce((a, b) => a + b, 0);
console.log(sum)

to split the value number into an array of digits.

And then we add the digits together with reduce.

To split the digits, we use toString to convert it to a string.

Then we call split with an empty string to split the string version of value into an array of digit strings.

Next, we call map with Number to map the digit strings back to numbers.

And then we use reduce to add them together.

Therefore, sum is 21.

Conclusion

To sum all the digits of a number JavaScript, we can use some array methods.