Category: JavaScript

Sometimes, we want to check if a specific pixel of an image is transparent with JavaScript.

In this article, we’ll look at how to check if a specific pixel of an image is transparent with JavaScript.

How to check if a specific pixel of an image is transparent with JavaScript?

To check if a specific pixel of an image is transparent with JavaScript, we can put the image in a canvas and then get the pixel data from the canvas.

For instance, we write

const img = document.getElementById("my-image");
const canvas = document.createElement("canvas");
canvas.width = img.width;
canvas.height = img.height;
canvas.getContext("2d").drawImage(img, 0, 0, img.width, img.height);

to select the image with getElementById.

And then we create a canvas with createElement.

We then set the canvas dimensions with

canvas.width = img.width;
canvas.height = img.height;

And then we call canvas.getContext("2d").drawImage to put the image into the canvas.

Next, in a click handler, we write

const pixelData = canvas
  .getContext("2d")
  .getImageData(event.offsetX, event.offsetY, 1, 1).data;

to get the clicked pixel’s data.

data is an array with the rgba values.

And we can get the transparency value from the last value, which is the a value.

Conclusion

To check if a specific pixel of an image is transparent with JavaScript, we can put the image in a canvas and then get the pixel data from the canvas.

Sometimes, we want to refresh an iframe using JavaScript.

In this article, we’ll look at how to refresh an iframe using JavaScript.

How to refresh an iframe using JavaScript?

To refresh an iframe using JavaScript, we call iframe.contentWindow.location.reload();.

For instance, we write

const iframe = document.getElementById("youriframe");
iframe.contentWindow.location.reload();

to get the iframe with getElementById.

Then we call iframe.contentWindow.location.reload to reload the iframe.

Conclusion

To refresh an iframe using JavaScript, we call iframe.contentWindow.location.reload();.

Sometimes, we want to fix string.split is not a function with JavaScript.

In this article, we’ll look at how to fix string.split is not a function with JavaScript.

How to fix string.split is not a function with JavaScript?

To fix string.split is not a function with JavaScript, we should make sure we’re calling split on a string.

For instance, we write

const string = document.location.toString();

to convert document.location to a string with toString before we call split on it.

Conclusion

To fix string.split is not a function with JavaScript, we should make sure we’re calling split on a string.

Sometimes, we want to reject promise and catch the error if status is not OK with fetch and JavaScript.

In this article, we’ll look at how to reject promise and catch the error if status is not OK with fetch and JavaScript.

How to reject promise and catch the error if status is not OK with fetch and JavaScript?

To reject promise and catch the error if status is not OK with fetch and JavaScript, we can check the response.ok property.

For instance, we write

const response = await fetch(url);
if (response.ok) {
  return response.json();
} else {
  throw new Error("Something went wrong");
}

to make a get request to url by calling fetch with url.

Then we check if response.ok with true from the promise returned.

If it is, then we return response body returned by response.json

Otherwise, we throw an error.

This code should be in an async function.

Conclusion

To reject promise and catch the error if status is not OK with fetch and JavaScript, we can check the response.ok property.

Sometimes, we want to truncate an array with JavaScript.

In this article, we’ll look at how to truncate an array with JavaScript.

How to truncate an array with JavaScript?

To truncate an array with JavaScript, we can use the array slice method.

For instance, we write

let arr = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
arr = arr.slice(0, 4);
console.log(arr);

to call arr.slice with 0 and 4 to get an array with the first 4 items of arr.

Then we assign the returned array back to arr to update it.

Conclusion

To truncate an array with JavaScript, we can use the array slice method.