Answers for "what is '...' in js"

what is javascript

Javascript is a scripting language that runs in the browser (also in your 
local environment with NodeJS)
JS is behind every action/interaction you have performed on the browser
With JS you can create web apps that will run on any machine with a browser

what is ... in javascript

function sum(...numbers) {
	return numbers.reduce((accumulator, current) => {
		return accumulator += current;
	});
};
 
sum(1,2) // 3
sum(1,2,3,4,5) // 15

what is javascript

// Function: creates a new paragraph and appends it to the bottom of the HTML body.

function createParagraph() {
  let para = document.createElement('p');
  para.textContent = 'You clicked the button!';
  document.body.appendChild(para);
}

/*
  1. Get references to all the buttons on the page in an array format.
  2. Loop through all the buttons and add a click event listener to each one.

  When any button is pressed, the createParagraph() function will be run.
*/

const buttons = document.querySelectorAll('button');

for (let i = 0; i < buttons.length ; i++) {
  buttons[i].addEventListener('click', createParagraph);
}