x = Symbol(3);

symbolObject[x]; // => undefined

// changing x back just creates another unique Symbol

x = Symbol(1);

symbolObject[x]; // => undefined

There are also well known symbols.

One of which is Symbol.iterator; if something implements

Symbol.iterator, it is iterable:

const x = [1, 2, 3, 4]; // x is an Array

are iterable

function should provide an iterator for x

xIterator.next(); // { value: 1, done: false }

xIterator.next(); // { value: 2, done: false }

xIterator.next(); // { value: 3, done: false }

xIterator.next(); // { value: 4, done: false }

xIterator.next(); // { value: undefined, done: true }

xIterator.next(); // { value: undefined, done: true }

// for..of loops automatically iterate values

for (const value of x) {

console.log(value); // 1 2 3 4

}

// Sets are also iterable:

[Symbol.iterator] in Set.prototype; // true

for (const value of new Set(['apple', 'orange'])) {

console.log(value); // "apple" "orange"

}