vanilla js check if element exists

javascript:(d=>{var css=`:root{background-color:#f1f1f1;filter:invert(1) hue-rotate(180deg)}img:not([src*=".svg"]),picture,video{filter: invert(1) hue-rotate(180deg)}`,style,id="dark-mode",ee=d.getElementById(id);if(null!=ee)ee.parentNode.removeChild(ee);else {style = d.createElement('style');style.type="text/css";style.id=id;if(style.styleSheet)style.styleSheet.cssText=css;else style.appendChild(d.createTextNode(css));(d.head||d.querySelector('head')).appendChild(style)}})(document)

/**
* Rewrites text
* @param {String} text The text to rewrite.
* @returns {Promise.<String[]>} Resolves into a list of about 10 rewritten versions. (Or rejects with an error)
* @example 
* var rewritten  = await rewrite("Sometimes I just want to code in JavaScript all day.");
* // ⇒ [
* //    "I sometimes just want to code JavaScript all day.",
* //    "JavaScript is my favorite programming language sometimes.",
* //    "I sometimes wish I could code in JavaScript all day.",
* //    "JavaScript is sometimes all I want to do all day.",
* //    "I like JavaScript sometimes and want to code all day long.",
* //    "Some days I just want to work all day in JavaScript.",
* //    "It's not uncommon for me to just want to code in JavaScript all day.",
* //    "My favorite thing to do sometimes is just code JavaScript all day.",
* //    "My favourite coding language is JavaScript, which I can code all day.",
*//     "JavaScript is my preferred language sometimes, since it lets me code all day.",
*// ];
*/
function rewrite(text) {
  return new Promise(async (resolve, reject) => {
    var { suggestions, error_code, error_msg, error_msg_extra } = await fetch(
      "https://api.wordtune.com/rewrite-limited",
      {
        headers: {
          accept: "*/*",
          "accept-language": "en-US,en;q=0.9",
          "content-type": "application/json",
          "x-wordtune-origin": "https://www.wordtune.com",
        },
        referrer: "https://www.wordtune.com/",
        body: JSON.stringify({
          action: "REWRITE",
          text: text,
          start: 0,
          end: text.length,
          selection: {
            wholeText: text,
            start: 0,
            end: text.length,
          },
        }),
        method: "POST",
      }
    ).then((res) => res.json());
    if (error_code || error_msg || error_msg_extra) {
      reject({
        code: error_code,
        message: error_msg,
        message_extra: error_msg_extra,
      });
    } else {
      resolve(suggestions);
    }
  });
}

$('.button').click(function(){

  var buttonId = $(this).attr('id');

  $('#modal-container').removeAttr('class').addClass(buttonId);

  $('body').addClass('modal-active');

})

​

$('#modal-container').click(function(){

  $(this).addClass('out');

  $('body').removeClass('modal-active');

});

$('.button').click(function(){

  var buttonId = $(this).attr('id');

  $('#modal-container').removeAttr('class').addClass(buttonId);

  $('body').addClass('modal-active');

})

​

$('#modal-container').click(function(){

  $(this).addClass('out');

  $('body').removeClass('modal-active');

});

var element = document.querySelectorAll('.elementClass');
if (typeof(element) != 'undefined' && element != null) {
    //your code here
}

<!-- JavaScript Bundle with Popper -->
<script src="https://cdn.jsdelivr.net/npm/bootstrap@5.0.0/dist/js/bootstrap.bundle.min.js" integrity="sha384-p34f1UUtsS3wqzfto5wAAmdvj+osOnFyQFpp4Ua3gs/ZVWx6oOypYoCJhGGScy+8" crossorigin="anonymous"></script>

var endExperiment = function() {

  prompt_resubmit = function() {
    replaceBody(error_message);
    $("#resubmit").click(resubmit);
  };

  resubmit = function() {
    replaceBody("<h1>Trying to resubmit...</h1>");
    reprompt = setTimeout(prompt_resubmit, 10000);
    
    psiTurk.saveData({
      success: function() {
          clearInterval(reprompt); 
      }, 
      error: prompt_resubmit
    });
  };
  // Load the debriefing page 
  psiTurk.showPage('debriefing.html');

  //code for bonus??
  $("#next").click(function () {
      record_responses();
      psiTurk.saveData({
            success: function(){
                psiTurk.computeBonus('compute_bonus', function() { 
                  psiTurk.completeHIT(); // when finished saving compute bonus, the quit
                }); 
            }, 
            error: prompt_resubmit});
  });

const mongoose = require('mongoose')
require('dotenv').config()

mongoose.connect(process.env.MONGODB_URI, {
   useNewUrlParser: true,
   useUnifiedTopology: true,
   useCreateIndex: true
})

mongoose.connection.on('connected', () => {
  console.log('Mongoose connected')
})

mongoose.connection.on('error', (err) => {
  console.log(`Mongoose connected error ${err}`)
})

mongoose.connection.on('disconnected', () => {
  console.log('Mongoose disconnected')
})

function getRandInt(start, end) {
    return Math.floor(Math.random() * (end - start + 1)) + start
}

    <input class="copy" type="text" value="copy this text">
    <button class="copy">copy</button>
    <input class="paste" type="text" value="paste here">
    <button class="paste">paste</button>

const inputCopy = document.querySelector('input.copy')
const btnCopy = document.querySelector('button.copy')
const inputPaste = document.querySelector('input.paste')
const btnPaste = document.querySelector('button.paste')

btnCopy.onclick = async () => {
    await navigator.clipboard.writeText(inputCopy.value)
    console.log('copied!');
}
btnPaste.onclick = async () => {
    const clipText = await navigator.clipboard.readText()
    inputPaste.value = clipText
    console.log('pasted!');
}

import React from 'react';
import Carousel from 'react-material-ui-carousel'
import { Paper, Button } from '@material-ui/core'

function Example(props)
{
    var items = [
        {
            name: "Random Name #1",
            description: "Probably the most random thing you have ever seen!"
        },
        {
            name: "Random Name #2",
            description: "Hello World!"
        }
    ]

    return (
        <Carousel>
            {
                items.map( (item, i) => <Item key={i} item={item} /> )
            }
        </Carousel>
    )
}

function Item(props)
{
    return (
        <Paper>
            <h2>{props.item.name}</h2>
            <p>{props.item.description}</p>

            <Button className="CheckButton">
                Check it out!
            </Button>
        </Paper>
    )
}

const str  = 'mycookie=test';

const spl = str.split(';');

const x = spl.map(v => v.split('='))
.map(([k, ...vs]) => [k, vs.join('=')]).reduce((acc, [k, v]) ={
       acc[k.trim()] = decodeURIComponent(v);
       return acc;
 }, {});

console.log(x);