rpivo

Creating a JSON Walker Class

class JsonWalker {
  constructor(content) {
    this.content = content;
  }

  get firstChild() {
 return new JsonWalker(this.content.children[0]);

rpivo

Implementing a Hot-Reloading Server

This native Node hot-reloading server implementation uses the EventSource Web API to unidirectionally send pings from the server to the client whenever the client should refresh the page. The server will send a ping whenever the source code is rebuilt.

On starting the server, the browser will automatically open at http://localhost:8000.

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First, you can add a serve script to package.json. This will run Server.js inside a util folder.

rpivo

Adding a Clean Script in Node

import fs from "fs";
import path from "path";

const cwd = process.cwd();

const assetsFolder = "assets";
const distFolder = "dist";

rpivo

Traverse All Subsets in an Array

In the below example, we create a function that's responsible for looping through an array. At each traversal, if we've reached the end of the array, we return x. Otherwise, we call the function again with i incremented, and with x added with the value of the array at index i.

function sum(arr, i = 0, x = 0) {
  return i === arr.length
    ? x
    : sum(arr, i + 1, x + arr[i]);
}

rpivo

Getting the Number of Subsets Within a Set

The number of subsets within a set will always be 2 ^ N, where N is the length of the set.

const a = [1, 2, 3];

console.log(2 ** 3); // 8

Below is the **power set** of the set `a`, or a representation of all the subsets with the set `a`.

rpivo

Create a MySQL Table Only if It Doesn't Already Exist

The following statement creates a MySQL table Products only if it doesn't yet exist. If the table does already exist, then the statement will do nothing.

CREATE TABLE IF NOT EXISTS Products (
  product_id int,
  low_fats ENUM('Y', 'N'),
  recyclable ENUM('Y', 'N')
);

rpivo

Declaring Enum Types in MySQL

The following statement creates a table Products that contains three columns: product_id, low_fats, and recyclable.

While product_id is of type int, both low_fats and recyclable are enums that can only be one of the declared values within the ENUM() clause ('Y' or 'N', in this case).

CREATE TABLE Products (
  product_id int,
 low_fats ENUM('Y', 'N'),

rpivo

Completely Emptying a MySQL Table With TRUNCATE TABLE

The following statement will create a new table Products and insert values into it.

CREATE TABLE IF NOT EXISTS Products (
  product_id int,
  low_fats ENUM('Y', 'N'),
  recyclable ENUM('Y', 'N')
);

rpivo

Using Order By to Sort MySQL Table Results by Ascending or Descending Order

The following statement will create a new table Products and insert values into it.

CREATE TABLE IF NOT EXISTS Products (
  product_id int,
  low_fats ENUM('Y', 'N'),
  recyclable ENUM('Y', 'N')
);

rpivo

Checking the Length of a String in a MySQL Where Clause

Let's say we have a SQL schema like this:

Create table If Not Exists Tweets(tweet_id int, content varchar(50));
Truncate table Tweets;
insert into Tweets (tweet_id, content) values ('1', 'Vote for Biden');
insert into Tweets (tweet_id, content) values ('2', 'Let us make America great again!');