Category: JavaScript

Sometimes, we want to add transitions to React styled components with JavaScript.

In this article, we’ll look at how to add transitions to React styled components with JavaScript.

How to add transitions to React styled components with JavaScript?

To add transitions to React styled components with JavaScript, we can change styles according to props.

For instance, we write:

import React from "react";
import styled, { css } from "styled-components";

const Button = styled.div`
  transform: rotate(0deg);
  transition: transform 0.2s ease-out;
  background: green;
  width: 50px;
  ${(props) =>
    props.expanded &&
    css`
      transform: rotate(45deg);
    `};
`;

export default function App() {
  const [expanded, setExpanded] = React.useState();

  React.useEffect(() => {
    setTimeout(() => {
      setExpanded(true);
    }, 2000);
  }, []);

  return <Button expanded={expanded}>hello</Button>;
}

to create a styled div and assign it to Button.

In it, we set the transform property to rotate the div according to the value of the expanded prop.

Then in App, we have the expanded state that’s set as the value of the expanded prop.

And we call setExpanded in the setTimeout callback 2 seconds after App is mounted.

Conclusion

To add transitions to React styled components with JavaScript, we can change styles according to props.

Sometimes, we want to validate date if is the last day of the month with JavaScript.

In this article, we’ll look at how to validate date if is the last day of the month with JavaScript.

How to validate date if is the last day of the month with JavaScript?

To validate date if is the last day of the month with JavaScript, we can check if the date plus 1 day is in the same month as the original date.

For instance, we write:

const isLastDay = (dt) => {
  const test = new Date(dt.getTime())
  const month = test.getMonth();
  test.setDate(test.getDate() + 1);
  return test.getMonth() !== month;
}

console.log(isLastDay(new Date(2022, 0, 1)))
console.log(isLastDay(new Date(2022, 0, 31)))

to define the isLastDay function that takes the JavaScript date dt.

In it, we create a copy of dt with new Date(dt.getTime()).

Then we get the month from test with getMonth.

Next, we call test.setDate to increment test‘s date by 1.

Then we check if test is the same month as dt with test.getMonth() !== month.

Therefore, the first console log logs false and the 2nd one logs true.

Conclusion

To validate date if is the last day of the month with JavaScript, we can check if the date plus 1 day is in the same month as the original date.

Sometimes, we want to create pause or delay in a JavaScript for loop.

In this article, we’ll look at how to create pause or delay in a JavaScript for loop.

How to create pause or delay in a JavaScript for loop?

To create pause or delay in a JavaScript for loop, we should use await with a for-of loop.

For instance, we write:

const wait = (ms) => new Promise(resolve => setTimeout(resolve, ms))

const loop = async () => {
  for (const a of [1, 2, 3]) {
    console.log(a)
    await wait(2000)
  }
}
loop()

to define the wait function that returns a promise that calls setTimeout with resolve to resolve the promise in ms milliseconds.

Then we define the loop function that runs a for-of loop to loop through an array.

In the loop body, we call wait with await to pause the loop for 2000 milliseconds before continuing to the next iteration.

As a result, we see that the numbers are logged after a 2 seconds delay between each iteration.

Conclusion

To create pause or delay in a JavaScript for loop, we should use await with a for-of loop.

Sometimes, we want to store Node.js fs.readfile’s result in a variable and pass to global variable with JavaScript.

In this article, we’ll look at how to store Node.js fs.readfile’s result in a variable and pass to global variable with JavaScript.

How to store Node.js fs.readfile’s result in a variable and pass to global variable with JavaScript?

To store Node.js fs.readfile’s result in a variable and pass to global variable with JavaScript, we can use the version of readFile that returns a promise.

For instance, we write:

const { promises: fs } = require('fs')
const read = async () => {
  const file = await fs.readFile('file.txt')
  console.log(file.toString())
}
read()

to import the promises version of fs with const { promises: fs } = require('fs').

Then we call fs.readFile with the file path.

And we get the read file handle with await and assign it to file.

Then we convert the file content to a string with toString.

Conclusion

To store Node.js fs.readfile’s result in a variable and pass to global variable with JavaScript, we can use the version of readFile that returns a promise.

Sometimes, we want to replace undefined with a empty string with JavaScript.

In this article, we’ll look at how to replace undefined with a empty string with JavaScript.

How to replace undefined with a empty string with JavaScript?

To replace undefined with a empty string with JavaScript, we can use the || operator to return a default if its left operand is undefined.

For instance, we write:

const s = undefined
const newS = s || 'hello'
console.log(newS)

We assign newS to s is s is truthy or 'hello' otherwise.

Since s is undefined, which is falsy, newSis‘hello’`.

Conclusion

To replace undefined with a empty string with JavaScript, we can use the || operator to return a default if its left operand is undefined.