Author: John Au-Yeung

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.

Sometimes, we want to fix the ‘A valid React element (or null) must be returned’ error with one of the component error in React and JavaScript.

In this article, we’ll look at how to fix the ‘A valid React element (or null) must be returned’ error with one of the component error in React and JavaScript.

How to fix the ‘A valid React element (or null) must be returned’ error with one of the component error in React and JavaScript?

To fix the ‘A valid React element (or null) must be returned’ error with one of the component error in React and JavaScript, we should make sure our React component returns one root node or fragment.

For instance, we write:

import React from "react";

export default function App() {
  return <div>hello world</div>;
}

to return one div.

Or:

import React from "react";

export default function App() {
  return <>hello world</>;
}

to return a fragment.

Conclusion

To fix the ‘A valid React element (or null) must be returned’ error with one of the component error in React and JavaScript, we should make sure our React component returns one root node or fragment.

Sometimes, we want to create random-salt-hash with crypto with Node.js and JavaScript.

In this article, we’ll look at how to create random-salt-hash with crypto with Node.js and JavaScript.

How to create random-salt-hash with crypto with Node.js and JavaScript?

To create random-salt-hash with crypto with Node.js and JavaScript, we can use the crypto.randomBytes method.

For instance, we write:

const crypto = require('crypto')
const buf = crypto.randomBytes(16);
console.log(buf)

We call crypto.randomBytes with 16 to create a buffer object with 16 random bytes.

Conclusion

To create random-salt-hash with crypto with Node.js and JavaScript, we can use the crypto.randomBytes method.