meaning of join in js code example

Example 1: javascript join array

var array = ["Joe", "Kevin", "Peter"];
array.join(); // "Joe,Kevin,Peter"
array.join("-"); // "Joe-Kevin-Peter"
array.join(""); // "JoeKevinPeter"
array.join(". "); // "Joe. Kevin. Peter"

Example 2: .join in javascript

const elements = ['Sun', 'Earth', 'Moon'];

console.log(elements.join());
// output: "Sun,Earth,Moon"

console.log(elements.join(''));
// output: "SunEarthMoon"

console.log(elements.join('-'));
// output: "Sun-Earth-Moon"