Category: JavaScript Answers

Sometimes, we want to get the index from a JSON object with value with JavaScript.

In this article, we’ll look at how to get the index from a JSON object with value with JavaScript.

How to get the index from a JSON object with value with JavaScript?

To get the index from a JSON object with value with JavaScript, we can use the array findIndex method.

For instance, we write:

const data = [{
  "name": "allFit",
  "section": "left"
}, {
  "name": "allbMatches",
  "section": "left"
}, {
  "name": "allOffers",
  "section": "left"
}, {
  "name": "allInterests",
  "section": "left"
}, {
  "name": "allResponses",
  "section": "left"
}, {
  "name": "divChanged",
  "section": "right"
}];

const val = "allInterests"
const index = data.findIndex((item) => {
  return item.name === val
});

console.log(index);

to call data.findIndex with a callback that finds the first item where the name property of an object in data is equal to val and returns the index of that object.

Therefore, index is 3 since the 4th object in data has name set to 'allInterests'.

Conclusion

To get the index from a JSON object with value with JavaScript, we can use the array findIndex method.

Sometimes, we want to retrieve file names out of a multi-file upload control with JavaScript.

In this article, we’ll look at how to retrieve file names out of a multi-file upload control with JavaScript.

How to retrieve file names out of a multi-file upload control with JavaScript?

To retrieve file names out of a multi-file upload control with JavaScript, we can get them from the change event’s files property.

For instance, we write:

<input type='file' multiple>

to add a file input that accepts multiple files.

Next, we write:

const input = document.querySelector("input");
input.onchange = (e) => {
  for (const f of e.target.files) {
    console.log(f.name)
  }
}

to select the file input with querySelector.

Then we set the input.onchange property to add a change event handler to the file input.

In it, we loop through the selected files with e.target.files with the for-of loop.

And then we get the file name of the selected file with f.name.

Conclusion

To retrieve file names out of a multi-file upload control with JavaScript, we can get them from the change event’s files property.

Sometimes, we want to convert data URL to image data with JavaScript.

In this article, we’ll look at how to convert data URL to image data with JavaScript.

How to convert data URL to image data with JavaScript?

To convert data URL to image data with JavaScript, we can create a canvas with the image.

For instance, we write:

const convertURIToImageData = (url) => {
  return new Promise((resolve, reject) => {
    if (!url) {
      return reject();
    }
    const canvas = document.createElement('canvas')
    const context = canvas.getContext('2d')
    const image = new Image();
    image.onload = () => {
      canvas.width = image.width;
      canvas.height = image.height;
      context.drawImage(image, 0, 0, canvas.width, canvas.height);
      resolve(context.getImageData(0, 0, canvas.width, canvas.height));
    }
    image.crossOrigin = "Anonymous";
    image.src = url;
  });
}
const url = "https://picsum.photos/200/300";
const load = async () => {
  const img = await convertURIToImageData(url)
  console.log(img)
}
load()

to create the convertURIToImageData function that takes a url.

In it, we return a promise that checks if the url is set.

If it’s not, we reject the promise.

Otherwise, we create a canvas with createElement.

Then we get its context with getContext.

Next, we create an img element with the Image constructor.

We set image.onload to a function to draws the image in the canvas bvy setting the canvas’ size to the image size.

Then we call drawImage to draw the image.

And then we call resolve with the image data we get from getImageData.

Next, we set image.crossOrigin to 'Anonymous' to let us get data from cross domain images.

And we src to url to load the image.

onload runs when the image is loaded.

Next, we define the load function that calls convertURIToImageData with url.

And then we get the img data from the promise with await.

Conclusion

To convert data URL to image data with JavaScript, we can create a canvas with the image.

Sometimes, we want to fix form onsubmit not working with JavaScript.

In this article, we’ll look at how to fix form onsubmit not working with JavaScript.

How to fix form onsubmit not working with JavaScript?

To fix form onsubmit not working with JavaScript, we can set the form’s onsubmit property to a function that’s run when we click the submit button.

For instance, we write:

<form>
  <input type="file" name="file">
  <input type="submit">
</form>

to add a form.

We add the submit button for the form with <input type="submit">.

Next, we write:

const form = document.querySelector('form')
form.onsubmit = (e) => {
  e.preventDefault()
  console.log('submitted')
}

to select the form with querySelector.

And then we set form.onsubmit to a function that calls preventDefault to stop the default server side behavior and log 'submitted'.

Therefore, when we click on Submit, we see 'submitted' logged.

Conclusion

To fix form onsubmit not working with JavaScript, we can set the form’s onsubmit property to a function that’s run when we click the submit button.

Sometimes, we want to use addEventListener and getElementsByClassName to pass the element ID to the event listener with JavaScript.

In this article, we’ll look at how to use addEventListener and getElementsByClassName to pass the element ID to the event listener with JavaScript.

How to use addEventListener and getElementsByClassName to pass the element ID to the event listener with JavaScript?

To use addEventListener and getElementsByClassName to pass the element ID to the event listener with JavaScript, we can use event delegation.

For instance, we write:

<ul>
  <li class="menu" id="bob">Robert Smith</li>
  <li class="menu" id="jane">Jane Doe</li>
  <li class="menu" id="sue">Susan Carter</li>
</ul>

to add an ul with some li elements.

Then we write:

document.onclick = (e) => {
  if (e.target.className === 'menu') {
    console.log(e.target.id)
  }
}

to set document.onclick to a function that checks the className of the clicked element.

If the className is 'menu', then we get the ID of the element we clicked on with e.target.id.

Conclusion

To use addEventListener and getElementsByClassName to pass the element ID to the event listener with JavaScript, we can use event delegation.