Useful Grammer/Snippets for JavaScript/Node.js


I would like to share some useful snippets for JavaScript coding!

🍮 String

Extract first xx characters

'Hello world!!'.substring(0,5); //=> "Hello"

🎉 Number

Covert a object value to number

Convert different object values to their numbers:

Number("1") // => 1

parseInt("100", 10); // => 100
parseFloat("0.405903"); // => 0.405903

A Proper Random Function

This TypeScript function always returns a random number between min and max (both included):

function getRndInteger(): number {
  const min = 1; // include
  const max = 10; // include
  return Math.floor(Math.random() * (max - min + 1) ) + min;
}

🐹 Date/Datetime

Convert Date object to String YYYYMMDD

function currentYYYMMDD() {
  const d = new Date();
  const year = String(d.getFullYear());
  let month = String(d.getMonth() + 1);
  if (month.length < 2) {
    month = `0${month}`;
  }
  let day = String(d.getDate());
  if (day.length < 2) {
    day = `0${day}`;
  }

  return `${year}${month}${day}`;
}

Convert String YYYYMMDD to Date

This is a example to convert String YYYYMMDD to date object:

function convertToDate(dateStr) {
  const year = dateStr.substring(0, 4);
  const month = dateStr.substring(4, 6);
  const day = dateStr.substring(6, 8);
  return new Date(year, month - 1, day);
}

Difference between two dates

Get difference like how many days between date 1 and date2:

// Calculate difference between two dates
function getDiffDays(date1, date2) {
  const timeDiff = date1.getTime() - date2.getTime();
  return Math.ceil(timeDiff / (1000 * 3600 * 24));
}

🐞 Array

some method

some method tests whether at least one element in the array passes the test implemented.

array.some(element => element % 2 === 0);

sort method

const arr = [1, 5, 8, 2, 4];
arr.sort((a, b) => a - b); // asc => [1, 2, 4, 5, 8]
arr.sort((a, b) => b - a); // desc => [8, 5, 4, 2, 1]

🏀 Object

count of keys

obj = {
  "hoge": "fuga",
  "pugi": "ugi"
}

var length = Object.keys(obj).length;
console.log(length); //=> 2

🍣 Files

Get all files in a directory in Node.js

const testFolder = "./tests/";
const fs = require("fs");

fs.readdirSync(testFolder).forEach(file => {
  console.log(file);
});

Check file/directory exists in Node.js

import * as fs from "fs";
if (fs.existsSync(path)) {
    // Do something
}

Remove all files in directory in Node.js

The following snippets is to removoe all files in directory without removing the directory itself using Node.js.

const fs = require('fs');
const path = require('path');

const directory = 'test';

fs.readdir(directory, (err, files) => {
  if (err) throw err;

  for (const file of files) {
    fs.unlink(path.join(directory, file), err => {
      if (err) throw err;
    });
  }
});

🚌 Etc

Extract the host from a URL

const url = require('url');
console.log(url.parse(x).hostname);

Get current file name

const path = require('path');
const scriptName = path.basename(__filename);

🐠 References

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