Category: JavaScript Answers

Sometimes, we want to set date in input type date with JavaScript.

In this article, we’ll look at how to set date in input type date with JavaScript.

How to set date in input type date with JavaScript?

To set date in input type date with JavaScript, we can set the valueAsDate property of the date input.

For instance, we write

document.getElementById("datePicker").valueAsDate = new Date();

to select the date input with getElementById.

Then we set its valueAsDate property to a date object with the current date time to set the date input’s value.

Conclusion

To set date in input type date with JavaScript, we can set the valueAsDate property of the date input.

Sometimes, we want to check if date between dates with Moment.js and JavaScript.

In this article, we’ll look at how to check if date between dates with Moment.js and JavaScript.

How to check if date between dates with Moment.js and JavaScript?

To check if date between dates with Moment.js and JavaScript, we can use the isBetween method.

For instance, we write

const compareDate = moment("15/02/2022", "DD/MM/YYYY");
const startDate = moment("12/01/2022", "DD/MM/YYYY");
const endDate = moment("15/01/2022", "DD/MM/YYYY");
const isBetween = compareDate.isBetween(startDate, endDate, "days", "()");

to call compareDate.isBetween with startDate and endDate to check is compareDate is between startDate and endDate when comparing days.

The last argument is the inclusivity value, which specifies we compare exclusively.

We can also use '(]' for right inclusive, '[)' for left inclusive, or '[]' for all inclusive.

Conclusion

To check if date between dates with Moment.js and JavaScript, we can use the isBetween method.

Sometimes, we want to create an array with random values with JavaScript.

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

How to create an array with random values with JavaScript?

To create an array with random values with JavaScript, we can use the Array constructor and the Math.random method.

For instance, we write

const arr = Array(40)
  .fill()
  .map(() => Math.round(Math.random() * 40));

to call Array with 40 to create an array with 40 empty slots.

Then we call fill to fill the slots with undefined.

And then we call map with a callback that returns a random number between 0 and 40 for each slot with Math.random rounded to the nearest integer with Math.round.

Conclusion

To create an array with random values with JavaScript, we can use the Array constructor and the Math.random method.

Sometimes, we want to use modulo operator (%) in JavaScript.

In this article, we’ll look at how to use modulo operator (%) in JavaScript.

How to use modulo operator (%) in JavaScript?

To use modulo operator (%) in JavaScript, we can use it to get the remainder when dividing a number by another.

For instance, we write

const remainder = 10 % 3;

to get the remainder when dividing 10 by 3.

remainder should be 1 since 10 divided by 3 has remainder 1.

Conclusion

To use modulo operator (%) in JavaScript, we can use it to get the remainder when dividing a number by another.

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.